Abstract
The Anninghe-Zemuhe-Xiaojiang fault zone (AZXFZ) is an important boundary fault zone on the southeastern margin of the Tibetan Plateau, with frequent strong earthquakes. Previous studies have imaged widespread low-velocity zones in this area. However, there are still many disputes on the connectivity and genesis of the low-velocity zones. In this study, we obtain the Rayleigh wave phase velocity dispersion curves at 4–25-s periods using observations from 378 broadband stations located near the AZXFZ. The new 3D S-wave velocity model has a lateral resolution of about 30 km in 0–35-km depth and is obtained by direct inversion of surface wave dispersion data. The new results clearly image two low-velocity zones and a high-velocity zone in the middle crust of the study region. The low-velocity zone on the western side of the Lijiang-Xiaojinhe fault is related to the eastward flow of crustal material and the movement of the left lateral strike-slip faults in the Tibetan Plateau, while the low-velocity anomaly distributed along the Daliangshan fault and Xiaojiang fault is the superimposition effect of shear heating of the faults and upwelling of mantle material. The uplift of Gongga Shan is a combination of the continuous accumulation of crustal material in the middle and lower crust of the southeastern margin of the Tibetan Plateau as well as the bending and compression of the Sichuan-Yunnan Block and the Xianshuihe-Anninghe fault zone.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
1 Introduction
High-resolution velocity structures provide important clues for studying the tectonic evolution of active blocks and geodynamic simulations (Bao et al., 2015; Fang et al., 2010; Huang et al., 2018; Shapiro et al., 2005; Yang et al., 2007). The velocity structure is an important factor in the propagation of earthquake ruptures (Ampuero & Vilotte, 2002; Huang & Ampuero, 2011; Huang et al., 2014; Jiang et al., 2021; Weng et al., 2016). Obtaining high-resolution velocity structures in fault zones plays an important role in determining the deep geometry, evolution processes and movement pattern of a fault. Accordingly, researchers have performed many dense portable array observations and studies to obtain the fine-scale velocity structure of fault zones, such as the San Jacinto fault (Lewis et al., 2005), Newport-Inglewood fault (Zhang & Langston, 2020), Tanlu fault (Luo et al., 2021), Chenghai fault (Jiang et al., 2021; Yang et al., 2020), etc.
The AZXFZ is located in the southeastern margin of the Tibetan Plateau (Fig. 1a, b), and it forms the eastern boundary of the Sichuan-Yunnan Block, one of the most seismically active large strike-slip fault systems in Southwest China (Xu et al., 2005; Zhang et al., 2013). This area has experienced a series of strong earthquakes with magnitude > 7.0 (Fig. 1b; Wen et al., 2000, 2008b; Yi et al., 2008), such as the 1480 Yuexi M7.5 earthquake, 1536 Xichang M7.5 earthquake and 1850 Xichang M7.5 earthquake. Previous studies found seismic gaps and locking features along the AZXFZ, based on studies of seismic activity and geodesy, indicating a high seismic hazard in the region (Jiang et al., 2015; Wen et al., 2008a; Yi et al., 2004, 2005; Zhao et al., 2015). The frequent strong seismic activity of the fault zone is inextricably linked to its deep structure, especially the relative motion of the blocks caused by the eastward escape of material from the Tibetan Plateau (Bao et al., 2015; Wang et al., 2017). As one of the channels for material flow within the Tibetan Plateau, in-depth studies of the fine 3D velocity structure of the crust in this region are of great significance for understanding the evolution processes of the Tibetan Plateau.
The uplift and deformation of the Tibetan Plateau are closely related to its deep tectonics (England & Housema, 1986; Houseman & England, 1993; Willett et al., 1993). Accordingly, researchers have used a variety of methods to study the deep structure of the AZXFZ and its surrounding areas, which have resulted in a series of important insights. The crust of the southeastern margin of the Tibetan Plateau has a high geothermal heat flow of 80 mW/m2 (Hu et al., 2000; Shi & Wang, 2017; Wang et al., 2014) and a high Poisson's ratio of > 0.28 (Wang et al., 2017). Many body wave, surface wave, receiver function and magnetotelluric inversion studies have further revealed the existence of low-velocity zones (Bao et al., 2015; Huang et al., 2018; Tan et al., 2018; Yao et al., 2008; Zhang et al., 2020; Zheng et al., 2016), complex anisotropy (Huang et al., 2010, 2018; Lu et al., 2014; Xie et al., 2013; Yao et al., 2010), high attenuation (Zhao et al., 2013) and high conductivity layers (Bai et al., 2010) in the middle and lower crust of the southeastern margin of the Tibetan Plateau. However, previous studies have different interpretations of the continuity and genesis of these low-velocity zones. Some tomography results show that the low-velocity zones are continuous along the eastern margin of the Tibetan Plateau and the Xianshuihe-Xiaojiang fault zone (Li et al., 2009; Ma et al., 2008; Wei et al., 2010). Meanwhile, other results show high-velocity anomalies around Panzhihua and Shimian-Xichang (Bao et al., 2015; Fan et al., 2015; Pan et al., 2015; Yao et al., 2008; Zhang et al., 2020). Some studies have suggested that crustal flow exists in the low-velocity zones (Bai et al., 2010; Clark & Royden., 2000; Liu et al., 2014; Royden et al., 1997) and propose that the crustal flow is not continuous within the southeastern margin of the Tibetan Plateau (Bao et al., 2015; Chen et al., 2014; Huang et al., 2018; Yao et al., 2008; Zhang et al., 2020). However, these low-velocity zones have also been suggested to be associated with shear heating of the faults or the upwelling of mantle material along the faults (Li et al. 2019b; Wu et al., 2013; Yang et al., 2020; Yu et al., 2022; Zhang et al., 2020). The high-resolution velocity structure is the key to revealing the continuity of the two low-velocity zones and its genesis because it directly affects whether the genesis of the eastern low-velocity zone is related to the eastward escape of material from the Tibetan Plateau. In addition, the Gongga Shan, located in the Longmenshan-Jinpingshan Orogenic Belt (Lai et al., 2006; Xu et al., 2007), shows significant differences from the Longmenshan in terms of both elevation and uplift rate. Researchers also have different views about the uplift mechanism of the Gongga Shan, such as the 'dynamic topography' model (Clark et al., 2005) and the 'transpression' model (Chen et al., 2008; He et al., 2008; Tan et al., 2010).
Due to sparse distribution of seismic stations, short observation time and different tomography methods, there are few high-resolution velocity models near the AZXFZ. Although previous studies have imaged two low-velocity zones, but the connectivity of the two low-velocity zones is not well resolved because of low resolution (Li et al., 2009; Ma et al., 2008; Wei et al., 2010). Some studies suggest that the genesis of the two low-velocity zones is related to crustal flow (Bao et al., 2015; Huang et al., 2018; Yao et al., 2008). In addition, the uplift mechanism of the Gongga Shan is also unclear. In this article, we processed seismic data recorded by four arrays deployed in the AZXFZ with ambient noise tomography. The high-resolution 3D S-wave velocity structure of the AZXFZ and its surrounding area was determined. In addition, we explore the relationship between the velocity structures and tectonic evolution processes, providing a new velocity model (AZX-CVM1.0, Anninghe-Zemuhe-Xiaojiang Community Velocity Model 1.0) for geodynamic studies of the southeastern Tibetan Plateau.
2 Data
We collect continuous waveform data recorded by 378 stations from four arrays: CXA, HMLYA, XCA and AZXA. The distribution of stations is shown in Fig. 1c, and array information is shown in Table 1.
The data processing method in this study are similar to those of Bensen et al. (2007) and mainly include (1) single station pre-processing, (2) cross-correlation calculation and stacking, (3) dispersion curve measurement and (4) dispersion curve quality control. First, we cut the raw data into 1-day length. Then, the raw data were pre-processed with resampling to 1 Hz, band-pass filtering (4–40 s), time-domain normalization and spectral whitening. Due to the different operation periods of the arrays, the data were subjected to cross-correlation calculation and linear stacking, respectively. The dispersion measurements were then performed using an image-based analysis technique method (Yao et al., 2004, 2005, 2006). To obtain reliable dispersion curves, we performed quality control with SNR > 3.0 and station spacing > 1.5 λ (Yao et al., 2011), where SNR is the signal-noise ratio and λ is the wavelength. Then, we selected dispersions with cluster analysis (Fang et al., 2010). A total of 13,746 Rayleigh wave phase velocity dispersions were finally obtained.
The noise cross-correlation functions for R3XC01 and other stations are shown in Fig. 2. Clear surface wave signals can be seen in the positive and negative segments. Figure 3 shows an example of a Rayleigh wave phase velocity dispersion curve for the R3XC01-R5DXY09 station pair. Figure 4 shows all dispersion curves and ray path numbers for 4–30-s periods. The average inter-station distance is 99 km, and most station pairs are within 200 km. Therefore, this study only used 4-25-s dispersion data for inversion. Figure 5 shows the distribution of ray paths for different periods. The ray paths of each period intersect with each other, with dense ray paths in the central part and low density of ray coverage at the periphery of the study region.
3 Methods
In this article, the one-step inversion method developed by Fang et al. (2015) is used to directly invert the S-wave velocity structure. The method considers the effect of the propagation effect of non-great circle paths of surface waves at different periods, which can effectively improve the inversion accuracy of short-period dispersion data. In recent years, this method has been well applied in the Taipei Basin, Tanlu fault and southeastern margin of the Tibetan Plateau to obtain high-resolution S-wave velocity structures (Fang et al., 2015; Li et al., 2016b; Luo et al., 2021; Zhang et al., 2018).
Compared with the traditional surface wave inversion method, the advantages of the direct inversion method are: (1) no intermediate step like constructing a two-dimensional group/phase velocity map is required, and the three-dimensional S-wave velocity structure can be obtained directly from a large amount of dispersion data, making the inversion more efficient. (2) The three-dimensional initial velocity model can be directly used. (3) The lateral variation of the structure can be better controlled. The basic principle of the method is as follows:
For points A and B, assume that the phase velocity between them is \(C_{AB} (\omega )\). Then, the traveltime \({\text{t}}_{AB} (\omega )\) from point A to point B is
where \({\text{L}}_{AB}\) is the length of the great circle path between A and B, \(S(l,\omega )\) is the slowness along \(l_{AB}\), and \({\text{S}}_{{\text{m}}} (\omega )\) is the high-frequency summation approximates.
The study area is divided into J grids, and each grid point can be represented by a one-dimensional model \(\Theta_{j}\), followed by a two-dimensional slowness distribution \({\hat{\text{S}}}_{{\text{m}}} (\omega )\) calculated with frequencies \(\omega\). The slowness of each grid point along the path \(l_{AB}\) can be obtained by bilinear interpolation, i.e., \(S_{m} (\omega ) = \sum\nolimits_{j = 1}^{J} {\upsilon_{mj} \hat{S}_{j} (\omega )}\), where \(\upsilon_{mj}\) is the bilinear interpolation coefficient, and the following \(v_{ij}\) is the same.
Then, the ith surface wave traveltime is
For the inverse problem, the objective is to minimize the differences between the observed time \(t_{i}^{obs} (\omega )\) and model prediction \(t_{i} (\omega )\), where the traveltime difference is
where \(C_{{\text{j}}}\) and \(\delta {C}_{j}(\omega )\) are the phase velocity and the perturbation at the jth grid point, respectively. \(\delta C_{{\text{j}}} \left( \omega \right)\) with the three variables of P-wave velocity, S-wave velocity and density related to the variation with depth z, respectively, rewrite Eq. (3) as
where \(\alpha_{j} (z)\),\(\beta_{j} (z)\), and \(\rho_{j} (z)\) are the P- and S-wave velocity and density, respectively, K is the number of grids at depth, and N = J×K is the total number of grids. Write Eq. (4) as a matrix form of the inversion problem
where d is the traveltime residual vector of the full frequencies and paths of the surface wave, G is the sensitivity matrix, and m is the model vector, whose expression is
Its solution can be obtained by solving for the minimum of the following equation
where the first term on the right-hand side of the equation is the \(L_{2}\)-norm of the data misfit, the second term is the \(L_{2}\)-norm of the model regularization, L is the model smoothing operator, and \(\lambda\) is the Lagrange operator.
In this study, the initial model is created by interpolating the 3D velocity model of Shen et al. (2016) with 0.15° × 0.15° grid size. As to depth, the maximum inversion depth can be set to 2–2.5 times the maximum period (Fang et al., 2015). As the vertical resolution decreases with increasing depth, the interval of the depth should gradually increase. The maximum period of the data in this study is 25 s. After checkerboard tests, our final inversion depth grid is set to be 1-km interval at 0–5 km depth, 2-km interval at 6–30 km depth and 5-km interval at 35–50 km depth. The final velocity structure is obtained by L-curve testing with a smoothing factor chosen to be 80 (Fig. 6a) and a total of 10 iterations. The standard deviation of traveltime residual is reduced from 1.25 s to 0.81 s (Fig. 6b). The mean value of the residual is also reduced to 0.014 s.
4 Results
4.1 Analysis of the Reliability of the Results
To analyze the resolution of the tomography results, the study area was divided into 0.3° × 0.3° grids with 2% (Fig. 7a–d) and 3% (Fig. 7e–h) random noise. The velocity perturbation was ± 5%, and the one-dimensional model was used for the checkerboard tests. The remaining parameters were the same as those in the inversion.
The checkerboard tests in Fig. 7 show good recovery at 5–35-km depth. The lateral resolution in this study is about 0.3° × 0.3°. Overall, the model recovery is correlated with the density of the ray paths. Because the ray paths are denser in the central part of the study area, the velocity anomaly is recovered better than at the periphery. Figure 7a–d and Fig. 7e–h show that the effect of recovery model with 3% noise is slightly worse than that with 2%, especially at the periphery. However, the checkerboard pattern can still be recovered well in the central of the study area.
To evaluate the reliability of the tomography results in this study, we compared the S-wave velocity with Zhang et al. (2020) for the same area and depth (Fig. 8). Zhang et al. (2020) used ambient noise data recorded at 132 permanent broadband stations with a lateral resolution of 1° × 1° at 0–70 km. Figure 8 shows that the general characteristics of the two models are similar, but the lateral resolution of our new model is significantly improved. At 10-km depth, both show high-velocity anomalies near Jiulong and Panzhihua and low-velocity anomalies in the Yanyuan Basin and Xichang Basin. However, the shape and velocity are slightly different. Our study shows a clear low-velocity anomaly near the Gongga Shan and a high-velocity zone along the Anninghe fault, corresponding to the location of mafic and ultramafic magma proposed by Zhang (1988). Figure 8c–d shows the low-velocity zones on the east and west sides of the study area, separated by the high-velocity zone near Emeishan-Panzhihua, with no connectivity between the two low-velocity zones in the study area. However, our result reveals clear velocity differences between the two sides of the Anninghe-Zemuhe fault zone. This shows that the model obtained in this study has a higher resolution and can reveal small-scale velocity anomalies than that of Zhang et al. (2020).
4.2 S-wave Velocity Structure
Figure 9 shows the S-wave velocity structure at different depths. At 5–8-km depth (Fig. 9a–b), a low-velocity anomaly appears near the Gongga Shan, similar to the low-velocity structure within 5–10-km depth obtained by Wang (2016). The areas around the Xichang Basin and Yanyuan Basin show significantly low-velocity anomalies, primarily influenced by the surface sediments. The Sichuan Basin, located in the northeastern corner of the study area, also exhibits a low-velocity anomaly in the shallow crust due to thick sediments (Bao et al., 2015; Yao et al., 2008; Zhang et al., 2020).
In mid-crust (12–24 km depth, Fig. 9c–e), the entire study area begins to show two low-velocity zones on the east and west sides (hereafter referred to as LV1 and LV2, respectively) of the high-velocity body in the middle. With increasing depth, the low-velocity anomaly in the Gongga Shan area is connected to LV1 and separated from the high-velocity zone on its eastern side by the southern section of the Xianshuihe fault and the Lijiang-Xiaojinhe fault. To the east of the study area, the middle and southern sections of the Daliangshan fault and the Xiaojiang fault are located in LV2. Several main faults in the northern part of the study area, such as the Lijiang-Xiaojinhe fault, the southern section of the Anninghe fault and the Zemuhe fault, have obvious east–west velocity contrasts, and the high- and low-velocity anomaly boundaries correspond more consistently with the fault boundaries. The overall characteristic of the Anninghe fault is high velocity, and the Shimian-Mianning section shows a more obvious high velocity compared with the Mianning-Xichang section. The Sichuan Basin overall presents a high-velocity anomaly. The area around Panzhihua shows high velocity, and this area gradually decreases with depth.
At 35 km (Fig. 9f), the lateral resolution decreases because of the small number of ray paths available. However, the high-velocity anomaly of the Sichuan Basin can still be observed as well as the low-velocity LV1 and LV2 separated by the high-velocity zone along the Emeishan-Panzhihua area.
Figure 10 shows the S-wave velocity profiles along 29.5°N, 28.6°N and 26.5°N (the locations of the profiles are marked in Fig. 9e). All three profiles show two low-velocity zones in the middle crust. Figure 10a indicates that there is a low-velocity anomaly beneath the Gongga Shan connected to LV1 in the middle crust, with a westward-dipping high-velocity structure in the east side. Figure 10b shows an arch-shaped high-velocity zone beneath the Lijiang-Xiaojinhe fault and the Daliangshan fault. Figure 10c indicates that there is a high-velocity anomaly with large area in Panzhihua, which may be related to magmatic activity in the Emeishan Large Igneous Province.
5 Discussion
5.1 The Genesis of LV1 and LV2
The new tomography results show two very significant low-velocity anomalies (LV1 and LV2) in the study area at 18–35-km depth (Figs. 9 and 10). The LV1 is confined by the Longmenshan fault and Lijiang-Xiaojinhe fault and is distributed in the western part of the study area. The LV2 is primarily distributed along the Daliangshan fault and Xiaojiang fault and their eastern sides. The two low-velocity zones extend to at least 35-km depth and are separated by a high-velocity anomaly around Shimian-Mianning-Xichang-Panzhihua area.
Previous tomography results using sparse seismic stations show that LV1 and LV2 are contiguous. Therefore, large-scale crustal flow is speculated to exist in the middle and lower crust of the southeastern margin of the Tibetan Plateau (Li et al., 2009; Ma et al., 2008; Wei et al., 2010). In recent years, with the deployment of portable seismic stations and new imaging algorithms, such as ambient noise tomography, the resolution of the velocity structure in the southeastern margin of the Tibetan Plateau has been greatly improved. Many studies have consistently revealed that there are two low-velocity zones or high-conductivity layers in the middle and lower crust (Bai et al., 2010; Bao et al., 2015; Chen et al., 2014; Fu et al., 2017; Huang et al., 2010, 2018; Li et al., 2016a, 2019b; Qiao et al., 2018; Wang et al., 2017; Xia et al., 2021; Yao et al., 2008; Yu et al., 2022; Zhang et al., 2020). The western low-velocity zone (LV1) extends northeastward along the Longmenshan fault, widely distributed in the Songpan-Ganzi Block, and extends southwestward to the Yunnan-Myanmar-Thailand Block. The other low-velocity zone (LV2) cuts off from the southwest side of the Sichuan Basin through the Daliangshan fault and Xiaojiang fault to the Red River fault.
Owing to the complex deformation processes on the southeastern margin of the Tibetan Plateau, controversies still exist concerning the genesis of LV1 and LV2. Some studies suggest that both LV1 and LV2 are caused by crustal flow (Huang et al., 2018; Yao et al., 2008; Zhao et al., 2013). The imaging results from Bai et al. (2010) and Bao et al. (2015) show that the boundary of the high-conductivity layers and low-velocity zones overlaps with the faults and suggest that the distribution of the two low-velocity channels may be related to the shearing of the faults. Other studies suggest that the genesis of LV2 is different from that of LV1 and may be related to shear heating of the faults (Li et al., 2019b; Yang et al., 2020; Zhang et al., 2020) and upwelling of mantle material (Wu et al., 2013; Li et al., 2019b; Yu et al., 2022).
GPS studies have obtained a clockwise-rotating velocity field around the Eastern Himalayan tectonics (Gan et al., 2007; Wang et al., 2001a; Zhang et al., 2004a). In addition, several surface wave azimuthal anisotropy studies have obtained a similar fast wave direction around LV1 (Lu et al., 2014; Wang et al., 2015; Yao et al., 2010; Yi et al., 2010), indicating the southeastward flow from the Tibetan Plateau. Leloup et al. (1999) showed that shear heating of faults can promote the melting of crustal material. In the crustal flow model, it is difficult for plateau material to sustain long distance flow via gravity alone (Bai et al., 2010). Shear heating of the faults can help reduce the strength of the crust and make it easier for crustal material to flow over long distances (Bao et al., 2015; Li et al., 2019b; Liu et al., 2014; Yang et al., 2020; Zhang et al., 2020). We speculate that left-lateral strike-slip faults such as the Xianshuihe fault and the Lijiang-Xiaojinhe fault in the LV1 region have a mutually reinforcing effect with the crustal flow.
The connectivity of the two low-velocity zones, LV1 and LV2, is a key factor that affects their genesis. If LV1 and LV2 are connected, their genesis may be similar, and both are influenced by crustal flow. However, if LV1 and LV2 are unconnected, the origin of LV2 cannot be interpreted with crustal flow exclusively. The new model (Figs. 9 and 10) clearly shows that LV1 and LV2 are unconnected and demonstrates that the low-velocity zones in the middle and lower crust are separated by the Anninghe-Zemuhe fault zone and the Panzhihua high-velocity zone, which are located in the middle and inner zones of the Emeishan Large Igneous Province. Because of the presence of a series of mafic and ultramafic magma from upper mantle (Zhang, 1988; Zhou et al., 2005), this high-velocity zone is strong enough to obstruct the continuous eastward flow of crustal material from LV1, making it impossible for plateau material to cross, resulting in LV1 and LV2 not being connected. This is inconsistent with the crustal flow model beneath the Anninghe-Zemuhe fault zone proposed by Zhu et al. (2017) and Yu et al. (2022). If LV1 and LV2 are connected, the low-velocity material possibly flows from the lower crust or upper mantle of Panzhihua or bypasses the Panzhihua high-velocity zone to the Xiaojiang fault via the Red River fault. Figs. 9 and 10c show that there is a high-velocity anomaly near Panzhihua from the surface to 35 km depth. Many tomography results indicate that this high-velocity anomaly extends from the crust to the upper mantle (Bao et al., 2015; Fan et al., 2015; Fang et al., 2022; Liu et al., 2021; Pan et al., 2015; Wu et al., 2013; Yang et al., 2014; Yao et al., 2008; Zhang et al., 2020). Therefore, it is unlikely that crustal material can flow from the bottom of the Panzhihua high-velocity anomaly to LV2.
Several surface wave azimuthal anisotropy results show that the fast wave directions in the middle and lower crust are consistent with the strike of the Red River fault and the Xiaojiang fault, respectively (Gao et al., 2020; Han et al., 2020). Positive radial anisotropy has also been found near these two faults (Huang et al., 2010; Yang et al., 2020). The Red River fault appears to possibly serve as a channel for material flow between the two low-velocity zones. However, the body wave tomography results show that the low-velocity anomalies are primarily concentrated in the northern and middle sections of the Red River fault, the northern section of the Xiaojiang fault and the southern section of the Xiaojiang fault, and there is a high-velocity zone at the intersection of the Xiaojiang fault and Red River fault (Deng et al., 2020; Wu et al., 2013; Xu et al., 2013). Ambient noise tomography results also show that the two low-velocity zones are not connected in the middle and lower crust through the Red River fault (Yao et al., 2008; Zhang et al., 2020). Li et al. (2016b) processed digital elevation model data and found that the middle and southern sections of the Red River fault uplift several hundreds of meters compared with its northern section, suggesting that the thickening of the crust is influenced by the flow of material from the middle crust. We believe that the plateau material from LV1 bypasses Panzhihua, passes through the Red River fault, but is then obstructed by the high-velocity zone in its southern section and does not flow to the Xiaojiang fault.
An increase in temperature generally leads to the reduction of S-wave velocity. According to Goes et al. (2000), when the temperature increases by 100 °C, the S-wave velocity reduces by 0.7–4.5%. According to the theoretical model of fault shear heating proposed by Leloup et al. (1999), the shear heating of fault occurs mainly along the fault, and the shear heating of the fault can affect 80 km on both sides of the fault. The slip rate of the fault is a key parameter that affects the temperature. For a slip rate of 10 mm/a, the temperature can increase by approximately 50 °C/a at a depth of 20 km. So, we infer that the shear heating contributes to the genesis of LV2. Compared with the average geothermal heat flow of 65 mW/m2 in Southwest Sichuan (Wang et al., 2001b; Xu et al., 2011), the surface heat flow increased by 10 mW/m2 and 20 mW/m2 on the eastern side of the Daliangshan fault and the northern section of Xiaojiang fault, respectively (Hu et al., 2000; Huang et al., 2018; Shi & Wang, 2017). The average amounts of slip of the Daliangshan fault and the northern section of the Xiaojiang fault are 3–4 mm/a (Wei et al., 2012) and 8–10 mm/a (Wen et al., 2011), respectively. The surface heat flows generated by the shearing movement of these faults are calculated theoretically to be approximately 6 mW/m2 and 15 mW/m2 (Leloup et al., 1999), respectively. Therefore, other factors need to be considered in addition to the increased surface heat flow resulting from the shearing movement of the fault. Because low velocity/high conductivity is found in the middle and lower crust near the Daliangshan fault and the northern section of the Xiaojiang fault and extends down to the upper mantle, many studies have proposed that the low-velocity structure in this region results from the upwelling of mantle material (Cheng et al., 2017; Lei et al., 2019; Li et al., 2019a; Wang et al., 2014; Wei et al., 2013; Yu et al., 2022). In addition, the negative radial anisotropy of the Daliangshan fault and the northern section of the Xiaojiang fault in the crust (Xie et al., 2017; Yang et al., 2020) reflect the possibility of mantle material upwelling in LV2. In summary, the shearing movements of the Daliangshan fault and Xiaojiang fault themselves can make the materials on both sides of the faults frictionally heat up and reduce the material strength of the middle crust. As with the upwelling of mantle material, this can result in the formation of a low-velocity zone with high heat flow.
5.2 The Uplift Mechanism of the Gongga Shan
Located between Kangding and Shimian, the Gongga Shan is adjacent to the Xianshuihe fault and Lijiang-Xiaojinhe fault. It has a height of approximately 7556 m, making it the highest peak on the eastern edge of the Tibetan Plateau. The Gongga Shan is currently ascending at a rate of 1–3 mm/a (Jiang et al., 2022; Liang et al., 2013; Pan & Shen., 2017). Different uplift mechanisms are proposed for the Gongga Shan. The 'dynamic topography' model and 'transpression' model are two possible end-members. The 'dynamic topography' model suggests that crustal flow existed in the middle and lower crust along the southeastern margin of the Tibetan Plateau. The flow of mechanically weak material through the Gongga Shan was blocked by the subduction of the Yangtze Block beneath it, which hindered the continuous eastward flow of plateau material and caused the uplift of the Gongga Shan (Clark et al., 2005). The 'transpression' model is based on the fact that in the Gongga Shan area, the fault direction of the Xianshuihe-Anninghe fault zone has changed to form an angle deviation with the moving direction of the Sichuan-Yunnan Block. The movement of the Sichuan-Yunnan Block can be decomposed into two components. One component corresponds to the slip motion of the faults; the other component causes compression on the Gongga Shan, which shortens the crust of the Gongga Shan area and results in vertical uplift (Chen et al., 2008).
As shown in Fig. 9d–f, at a depth of 18–35 km, the Gongga Shan exhibits a low-velocity anomaly located in the LV1. Figures 9 and 10a show that a high-velocity anomaly exists on the east of the Gongga Shan at 10–35-km depth. P-wave traveltime tomography and magnetotelluric imaging have identified a west-dipping high-velocity zone and high-conductivity layer in the middle and lower crust to the eastern side of the Gongga Shan (Jiang et al., 2022; Wang et al., 2021). Many studies indicate that the Yangtze Block subducted to the Songpan-Ganzi Block during the Oligocene (30–25 Ma; Cai et al., 1996; Guo et al., 2013; Xu et al., 2007). Xu et al. (2007), after mica 40Ar-39Ar dating from detachment faults, concluded that the shortening and deformation along the Longmenshan-Jinpingshan Orogenic Belt are related to the westward subduction of the Yangtze Block and the flow of the middle and lower crust (Royden et al., 1997; Xu et al., 1999). Therefore, the high-velocity zone within the middle crust on the eastern side of the Gongga Shan is likely a remnant of the westward subduction of the Yangtze Block, and this high-strength material is able to block eastward flow of the crustal material.
The Gongga Shan has many hot springs and high heat flow (Hochstein & Regenauer-Lieb., 1998; Shen et al., 2007). Isotope dating of zircon samples suggests that due to the east–west compressional movement of blocks (Mattauer et al., 1992) and the shearing movement of the fault (Liu et al., 2006; Wang et al., 1997), the southeastern section of the Xianshuihe fault underwent high-temperature metamorphism during the Miocene (18–12 Ma). The Gongga Shan granite beneath the sediments was the product of partial melting of crust formed under high-temperature conditions during this phase (Li et al., 1983; Li & Zhang., 2013). Many petrological and geochemical studies indicate that cooling of the molten material in the Gongga Shan occurred at 11–2 Ma (Lai et al., 2006, 2007; Li & Zhang, 2013; Roger et al., 1995; Xu & Kamp, 2000). Ar–Ar thermochromological study shows that the time of cooling to 300–400 °C in the southeastern section of the Xianshuihe fault is 3.6 Ma (Chen et al., 2006). Lai et al. (2007) simulated the thermal evolution history of apatite samples and concluded that the cooling rate of the Gongga granite in the early stage was extremely low. It started to cool rapidly at 55–70 °C/Ma until approximately 2 Ma years ago. At present, the Gongga Shan is still in the cooling period (Tan et al., 2010), and the rock strength is very low. That is why the Gongga Shan is imaged as a low-velocity anomaly at 0–12 km depth compared with the surrounding areas (Fig. 9a-c, 10a). Our tomography results (Fig. 9) show that the boundaries of high- and low-velocity zones coincide with large strike-slip faults, especially in the southeastern section of the Xianshuihe fault. Many studies have shown that the Xianshuihe fault underwent strong left lateral strike-slip shearing at 12–10 Ma (Chen et al., 2006; Roger et al., 1995; Zhang et al., 2004b). Then, influenced by the eastward flow of the crustal material, the fault strikes of the southeastern section of the Xianshuihe fault and the northern section of the Anninghe fault changed by approximately 20° from NW–SE to N-S. The movement direction of the Sichuan-Yunnan Block was consistent with the strike of the Xianshuihe fault, but inconsistent with the Anninghe fault. The change in the fault strike was able to resolve into an extrusion force on the Gongga Shan (Chen et al., 2008; Jiang et al., 2022; Tan et al., 2010). We conjecture that the weak upper crust of the Gongga Shan is prone to shorten in horizontal direction and to uplift vertically (Wen & Bai., 1985).
In summary, we considered the uplift mechanism of the Gongga Shan is as follows. Due to the eastward flow of the middle and lower crust of the Tibetan Plateau and obstruction of the strong Yangtze Block, the low-velocity and high-temperature materials beneath the Gongga Shan continued to accumulate and the crust further thickened, forming the gentle western side and steep eastern side of the Gongga Shan. Both 'dynamic topography' model and 'transpression' model contribute to the uplift of the Gongga Shan.
6 Conclusions
In this study, we obtain a new high-resolution 3D S-wave velocity model (AZX-CVM1.0) of the upper and middle crust in the Anninghe-Zemuhe-Xiaojiang fault zone with new observation data and direct surface wave inversion method. The lateral resolution of the tomography result near the fault zone is significantly improved. The main conclusions are as follows.
-
1.
Two distinct low-velocity zones are observed in the middle crust of the study area, separated by the Anninghe-Zemuhe fault zone and the Panzhihua high-velocity zone in the central area. This high-velocity anomaly strip may be related to the intrusion of high-density mafic and ultramafic magma at different depths in the lithosphere during the uplift of the mantle plume.
-
2.
The two low-velocity zones (LV1 and LV2) are not connected and have different genesis. The western low-velocity zone (LV1) is formed by the flow of material from the Tibetan Plateau, which is driven by gravity and shearing movement of the faults. The formation of the low-velocity anomaly (LV2) near the Daliangshan fault and Xiaojiang fault is a combination of shear heating by the faults and upwelling of mantle material.
-
3.
The Gongga Shan exhibits a low-velocity anomaly at 0–35-km depth. A high-velocity zone is imaged in the middle and lower crust on the east side of the Gongga Shan. It is speculated that the rapid uplift of the Gongga Shan is the superimposition effect of the accumulation of the plateau material and the bending and compression of the left-lateral strike slip faults in the block boundary.
Data availability
Data are available upon request from the authors. The AZX-CVM1.0 model can be downloaded at https://www.researchgate.net/publication/368829545_AZX-CVM10.
References
Ampuero, J. P., Vilotte, J. P., & Sánchez-Sesma, F. J. (2002). Nucleation of rupture under slip dependent friction law: Simple models of fault zone. Journal of Geophysical Research, 107(B12), 2324. https://doi.org/10.1029/2001JB000452
Bai, D. H., Unsworth, M. J., Meju, M. A., Ma, X. B., Teng, J. W., Kong, X. R., Sun, Y., Sun, J., Wang, L. F., Jiang, C. S., Zhao, C. P., Xiao, P. F., & Liu, M. (2010). Crustal deformation of the eastern Tibetan plateau revealed by magnetotelluric imaging. Nature Geoscience, 3, 358–362.
Bao, X. W., Sun, X. X., Xu, M. J., Eaton, D. W., Song, X. D., Wang, L. S., Ding, Z. F., Mi, N., Li, H., Yu, D. Y., Huang, Z. C., & Wang, P. (2015). Two crustal low-velocity channels beneath SE Tibet revealed by joint inversion of Rayleigh wave dispersion and receiver functions. Earth and Planetary Science Letters, 415, 16–24.
Bensen, G. D., Ritzwoller, M. H., Barmin, M. P., Levshin, A. L., Lin, F., Moschetti, M. P., Shapiro, N. M., & Yang, Y. (2007). Processing seismic ambient noise data to obtain reliable broad-band surface wave dispersion measurements. Geophysical Journal International, 169, 1239–1260.
Cai, X. L., Wei, X. G., Liu, C. Y., & Cao, J. M. (1996). On wedge-in orogeny-on the example of the Longmenshan orogenic belt. Acta Geologica Sichuan (in Chinese), 2, 97–102.
Chen, W., Zhang, Y., Zhang, Y. Q., Jin, G. S., & Wang, Q. L. (2006). Late Cenozoic episodic uplifting in southeastern part of the Tibetan Plateau-evidence from Ar-Ar thermochronology. Acta Petrologica Sinica, 22(4), 867–872.
Chen, G. H., Xu, X. W., Wen, X. Z., & Wang, Y. L. (2008). Kinematical transformation and slip partitioning of northern to eastern active boundary belt of Sichuan-Yunnan Block. Seismology and Geology (in Chinese), 30(1), 58–85.
Chen, M., Huang, H., Yao, H. J., van der Hilst, R., & Niu, F. L. (2014). Low wave speed zones in the crust beneath SE Tibet revealed by ambient noise adjoint tomography. Geophysical Research Letters., 41(2), 334–340.
Cheng, Y. Z., Tang, J., Cai, J. T., Chen, X. B., Dong, Z. Y., & Wang, L. B. (2017). Deep electrical structure beneath the Sichuan-Yunnan area in the eastern margin of the Tibetan plateau. Chinese Journal of Geophysics (in Chinese), 60(6), 2425–2441.
Clark, M. K., & Royden, L. H. (2000). Topographic ooze: Building the eastern margin of Tibet by lower crustal flow. Geology, 28(8), 703–706.
Clark, M. K., Bush, J. W. M., & Royden, L. H. (2005). Dynamic topography produced by lower crustal flow against rheological strength heterogeneities bordering the Tibetan Plateau. Geophysical Journal International, 162, 575–590.
Deng, S. Q., Zhang, W. B., Yu, X. W., Song, Q., & Wang, X. N. (2020). Analysis on crustal structure characteristics of southern Sichuan-Yunnan by regional double-difference seismic tomography. Chinese Journal of Geophysics (in Chinese), 63(10), 3653–3668.
England, P., & Houseman, G. (1986). Finite strain calculations of continental deformation: 2. Comparison with the India-Asia collision zone. Journal of Geophysical Research: Solid Earth, 91, 3664–3676.
Fan, L. P., Wu, J. P., Huang, L. H., & Wang, W. L. (2015). The characteristic of Rayleigh wave group velocities in the southeastern margin of the Tibetan Plateau and its tectonic implications. Chinese Journal of Geophysics (in Chinese), 58(5), 1555–1567.
Fang, L. H., Wu, J. P., Ding, Z. F., & Panza, G. F. (2010). High resolution Rayleigh wave group velocity tomography in North China from ambient seismic noise. Geophysical Journal International, 181, 1171–1182.
Fang, H. J., Yao, H. J., Zhang, H. J., Huang, Y. C., & van der Hilst, R. D. (2015). Direct inversion of surface wave dispersion for three-dimensional shallow crustal based on ray tracing: Methodology and application. Geophysical Journal International, 201(3), 1251–1263.
Fang, H. J., Liu, Y., Yao, H. J., & Zhang, H. J. (2022). Regional-scale joint seismic body-and surface-wave travel time tomography. Reviews of Geophysics and Planetary Physics (in Chinese), 54, 1–18. https://doi.org/10.19975/j.dqyxx.2022-055
Fu, V. Y., Gao, Y., Li, A., Li, L., & Chen, A. (2017). Lithospheric structure of the southeastern margin of the Tibetan Plateau from Rayleigh wave tomography. Journal of Geophysical Research: Solid Earth, 122, 4631–4644. https://doi.org/10.1029/2016JB013096
Gan, W. J., Zhang, P. Z., Shen, Z. K., Niu, Z. J., Wang, M., Wan, Y. G., Zhou, D. M., & Chen, J. (2007). Present-day crustal motion within the Tibetan Plateau inferred from GPS measurements. Journal of Geophysical Research: Solid Earth, 112(B8), B08416. https://doi.org/10.1029/2005JB004120
Gao, Y., Shi, Y. T., & Wang, Q. (2020). Seismic anisotropy in the southeastern margin of the Tibetan Plateau and its deep tectonic significances. Chinese Journal of Geophysics (in Chinese), 60(3), 802–816.
Goes, S., Govers, R., & Vacher, P. (2000). Shallow mantle temperatures under Europe from P and S wave tomography. Journal of Geophysical Research: Solid Earth, 105(B5), 11153–11169.
Guo, X. Y., Gao, R., Keller, G. R., Xu, X., Wang, H. Y., & Li, W. H. (2013). Imaging the crustal structure beneath the eastern Tibetan Plateau and implications for the uplift of the Longmen Shan range. Earth and Planetary Science Letters, 379, 72–80.
Han, C. R., Xu, M. J., Huang, Z. C., Wang, L. S., Xu, M. J., Mi, N., Yu, D. Y., Gou, T., Wang, H. B., Hao, S. J., Tian, M. Y., & Bi, Y. J. (2020). Layered crustal anisotropy and deformation in the SE Tibetan plateau revealed by Markov-Chain-Monte-Carlo inversion of receiver functions. Physics of the Earth and Planetary Interiors, 306, 106522.
He, H. L., Ikeda, Y., He, Y. L., Togo, M., Chen, J., Chen, C. Y., Tajikara, M., Echigo, T., & Okada, S. (2008). Newly-generated Daliangshan fault zone-Shortcutting on the central section of Xianshuihe-Xiaojiang fault system. Science in China Series D: Earth Sciences (in Chinese), 51(9), 1248–1258. https://doi.org/10.1007/s11430-008-0094-4
Hochstein, M. P., & Regenauer-Lieb, K. (1998). Heat generation associated with collision of two plates: The Himalayan geothermal belt. Journal of Volcanology and Geothermal Research, 83(1), 75–92.
Houseman, G., & England, P. (1993). Crustal thickening versus lateral expulsion in the Indian-Asian continental collision. Journal of Geophysical Research: Solid Earth, 10, 12233–12249.
Hu, S. B., He, L. J., & Wang, J. Y. (2000). Heat flow in the continental area of China: A new data set. Earth and Planetary Science Letters, 179, 407–419.
Huang, Y., & Ampuero, J. P., (2011). Pulse-like ruptures induced by low-velocity fault zones. Journal of Geophysical Research, 116(B12), 307. https://doi.org/10.1029/2011JB008684
Huang, H., Yao, H., & van der Hilst, R. D. (2010). Radial anisotropy in the crust of SE Tibet and SW China from ambient noise interferometry. Geophysical Research Letters, 37, L21310.
Huang, Y., Ampuero, J. P., & Helmberger, D. V. (2014). Earthquake ruptures modulated by waves in damaged fault zones. Journal of Geophysical Research, 119, 3133–3154. https://doi.org/10.1002/2013JB010724
Huang, Z. C., Wang, L. S., Xu, M. J., & Zhao, D. P. (2018). P wave anisotropic tomography of the SE Tibetan Plateau: Evidence for the crustal and upper-mantle deformations. Journal of Geophysical Research: Solid Earth, 123, 8957–8978.
Jiang, G. Y., Xu, X. W., Chen, G. H., Liu, Y. J., Fukahata, Y., Wang, H., Yu, G. H., Tan, X. B., & Xu, C. J. (2015). Geodetic imaging of potential seismogenic asperities on the Xianshuihe-Anninghe-Zemuhe fault system, southwest China, with a new 3-D viscoelastic interseismic coupling model. Journal of Geophysical Research: Solid Earth, 120, 1855–1873. https://doi.org/10.1002/2014JB011492
Jiang, X. H., Hu, S. Q., & Yang, H. F. (2021). Depth extent and Vp/Vs ratio of the Chenghai fault zone, Yunnan, China constrained from dense-array-based teleseismic receiver functions. Journal of Geophysical Research: Solid Earth, 126, e2021JB022190. https://doi.org/10.1029/2021JB022190
Jiang, F., Chen, X. B., Unsworth, M. J., Cai, J. T., Han, B., Wang, L. F., Dong, Z. Y., Cui, T. F., Zhan, Y., Zhao, G. Z., & Tang, J. (2022). Mechanism for the uplift of Gongga Shan in the Southeastern Tibetan Plateau Constrained by 3D magnetotelluric Data. Geophysical Research Letters, 49(9), e2021GL097394. https://doi.org/10.1029/2021GL097394
Lai, Q. Z., Ding, L., Wang, H. W., Yue, Y. H., & Cai, F. L. (2006). Thermal history check and supervision of apatite fission-track in the expand process of eastern margin of Qinghai-Xizang Plateau. Science in China Series d: Earth Sciences (in Chinese), 36(9), 785–796.
Lai, Q. Z., Ding, L., Wang, H. W., Yue, Y. H., & Cai, F. L. (2007). Constraining the stepwise migration of the eastern Tibetan Plateau margin by apatite fission track thermochronology. Science in China Series D Earth Sciences, 36(9), 785–796.
Leloup, P. H., Ricard, Y., Battaglia, J., & Lacassin, R. (1999). Shear heating in continental strike-slip shear zones: Model and field examples. Geophysical Journal International, 136, 19–40.
Lewis, M. A., Peng, Z., Ben-Zion, Y., & Vernon, F. L. (2005). Shallow seismic trapping structure in the San Jacinto fault zone near Anza. California. Geophysical Journal International, 162(3), 867–881.
Li, H., & Zhang, Y. (2013). Zircon U-Pb geochronology of the Konggar granitoid and migmatite: Constraints on the Oligo-Miocene tectono-thermal evolution of the Xianshuihe fault zone, East Tibet. Tectonophysics, 606, 127–139.
Li, H. Y., Su, W., Wang, C. Y., & Huang, Z. X. (2009). Ambient noise Rayleigh wave tomography in western Sichuan and eastern Tibet. Earth and Planetary Science Letters, 282, 201–211.
Li, C. Y., Jiang, X. D., Li, D. Y., Gong, W., & Mi, C. Y. (2016a). Tectonic uplift and its regime in the central southern segment of the Red River fault zone since Pliocene. Periodical of Ocean University of China (in Chinese), 46(7), 90–98.
Li, C., Yao, H. J., Fang, H. J., Huang, X. L., Wan, K., Zhang, H. J., & Wang, K. D. (2016b). 3D near-surface shear-wave velocity structure from ambient-noise tomography and borehole data in the Hefei Urban Area, China. Seismological Research Letters, 87(4), 882–892.
Li, D. H., Ding, Z. F., Wu, P. P., Liang, M. J., Wu, P., Gu, Q. P., & Kang, Q. Q. (2019a). Deep structure of the Zhaotong and Lianfeng fault zones in the eastern segment of the Sichuan-Yunnan border and the 2014 Ludian Ms65 earthquake. Chinese Journal of Geophysics (in Chinese), 62(12), 4571–4587.
Li, X., Bai, D. H., Ma, X. B., Chen, Y., Varentsov, I. M., Xue, G. Q., Xue, S., & Lozovsky, I. (2019b). Electrical resistivity structure of the Xiaojiang strike-slip fault system (SW China) and its tectonic implications. Journal of Asian Earth Sciences, 176, 57–67.
Li, Z. W., Chen, J. L., Hu, F. D., & Wang, M. L., (1983). Geologic structure of Gongga Mountainous Region. In: Chengdu Institute of Geography, Chinese Academy of Sciences (eds). Region Geographic Expedition in the Gongga Mountain. Chongqing Branch of Scientific and Technology Document Press, Chongqing (in Chinese).
Liang, S. M., Gan, W. J., Shen, C. Z., Xiao, G. R., Liu, J., Chen, W. T., Ding, X. G., & Zhou, D. M. (2013). Three-dimensional velocity field of present-day crustal motion of the Tibetan Plateau derived from GPS measurements. Journal of Geophysical Reasearch: Solid Earth, 119(10), 5722–5732.
Liu, S. W., Wang, Z. Q., Yan, Q. R., Li, Q. G., Zhang, D. H., & Wang, J. G. (2006). Timing, petrogenesis and geodynamic significance of Zheduoshan Granitoids. Acta Petrologica Sinica (in Chinese), 22(2), 343–352.
Liu, Q. Y., Van Der Hilst, R. D., Li, Y., Yao, H. J., Chen, J. H., Guo, B., Qi, S. H., Wang, J., Huang, H., & Li, S. C. (2014). Eastward expansion of the Tibetan Plateau by crustal flow and strain partitioning across faults. Nature Geoscience, 7(5), 361–365.
Liu, Y., Yao, H. J., Zhang, H. J., & Fang, H. J. (2021). The community velocity model vol 1.0 of Southwest China, constructed from joint body- and surface-wave travel-time tomography. Seismological Research Letters, 92, 2972–2987. https://doi.org/10.1785/0220200318
Lu, L. Y., He, Z. Q., Ding, Z. F., & Wang, C. Y. (2014). Azimuth anisotropy and velocity heterogeneity of Yunnan area based on seismic ambient noise. Chinese Journal of Geophysics (in Chinese), 57(3), 822–836.
Luo, S., Yao, H. J., Wang, J. N., Wang, K. D., & Liu, B. (2021). Direct inversion of surface wave dispersion data with multiple-grid parametrizations and its application to a dense array in Chao Lake, eastern China. Geophysical Journal International, 225(2), 1432–1452.
Ma, H. S., Zhang, G. M., Wen, X. Z., Zhou, L. Q., & Shao, Z. G. (2008). 3-D P wave velocity structure tomographic inversion and its tectonic interpretation in southwest China. Earth Science-Journal of China University of Geosciences (in Chinese), 33(5), 591–602.
Mattauer, M., Malavieille, J., Calassou, S., Lancelot, J., Roger, F., Hao, Z. W., Xu, Z. Q., & Hou, L. W. (1992). La chaîne triasique de Songpan-Garze (ouest Sechuan et Est Tibet): une chaîne de plissement-décollement sur marge passive Comptes rendus de l’Académie des sciences Série II. Mechanics, 314(6), 619–626.
Pan, Y. J., & Shen, W. B. (2017). Contemporary crustal movement of southeastern Tibet: Constraints from dense GPS measurements. Scientific Reports, 7, 45348. https://doi.org/10.1038/srep45348
Pan, J. T., Li, Y. H., Wu, Q. J., & Ding, Z. F. (2015). Phase velocity maps of Rayleigh waves in the southeast Tibetan Plateau. Chinese Journal of Geophysics (in Chinese), 58(11), 3993–4006.
Qiao, L., Yao, H., Lai, Y. C., Huang, B. S., & Zhang, P. (2018). Crustal structure of southwest China and northern Vietnam from ambient noise tomography: Implication for the large-scale material transport model in SE Tibet. Tectonics, 37, 1492–1506.
Roger, F., Calassou, S., Lancelot, J., Malavieille, J., Mattauer, M., Xu, Z. P., Hao, Z. W., & Hou, L. W. (1995). Miocene emplacement and deformation of the Konga Shan granite (Xianshui He fault zone, west Sichuan, China): Geodynamic implications. Earth and Planetary Science Letters, 130, 201–216.
Royden, L. H., Burchfiel, B. C., King, R. W., Wang, E., Chen, Z. L., Shen, F., & Liu, Y. P. (1997). Surface deformation and lower crustal flow in eastern Tibet. Science, 276, 788–790.
Shapiro, N. M., Campillo, M., Stehly, L., & Ritzwoller, M. H. (2005). High-resolution surface-wave tomography from ambient seismic noise. Science, 307(5715), 1615–1618.
Shen, W., Ritzwoller, M. H., Kang, D., Kim, Y. H., Lin, F. C., Ning, J. Y., Wang, W. T., Zheng, Y., & Zhou, L. Q. (2016). A seismic reference model for the crust and uppermost mantle beneath China from surface wave dispersion. Geophysical Journal International, 206, 954–979. https://doi.org/10.1093/gji/ggw175
Shen, L. C., (2007). The study of deep source CO2 degasification and carbon cycle in the southwest of China. Southwest University (in Chinese).
Shi, Z., & Wang, G. (2017). Evaluation of the permeability properties of the Xiaojiang Fault Zone using hot springs and water wells. Geophysical Journal International, 209, 1526–1533.
Tan, X. B., Xu, X. W., Li, Y. X., Chen, G. H., & Wan, J. L. (2010). Apatite fission track evidence for rapid uplift of the Gongga Mountain and discussion of its mechanism. Chinese Journal of Geophysics (in Chinese), 53(8), 1859–1867.
Tan, X. L., Fang, L. H., Wang, W. L., & Wu, J. P. (2018). Rayleigh wave group velocity tomography with ambient noise in the Anninghe-Zemuhe Fault Zone and its surrounding areas. Earthquake Research in China (in Chinese), 34(3), 400–413.
Wang, W. P., (2016). The application of double-difference tomography method in the intersection zone of Xianshuihe fault, Anninghe fault and Longmenshan fault. Institute of Geophysics, China Earthquake Administration (in Chinese).
Wang, Z. X., Xu, Z. Q., & Yang, T. N. (1997). Origin of the Zheguoshan granite and its tectonic setting. Journal of Chengdu University of Technology (in Chinese), 24(1), 48–55.
Wang, Q., Zhang, P. Z., Jeffrey, T. F., Roger, B., Kristine, M. L., Lai, X. A., You, X. Z., Nou, Z. J., Wu, J. C., Li, Y. X., Liu, J. N., Yang, Z. Q., & Chen, Q. Z. (2001a). Present-day crustal deformation in China constrained by global positioning system measurements. Science, 294(5542), 574–577. https://doi.org/10.1126/science.1063647
Wang, Y., Wang, J. Y., Xiong, L. P., Deng, J., & F. (2001b). Lithospheric geothermics of major geotectonic units in China mainland. Acta Geoscientia Sinica (in Chinese), 22(1), 17–22.
Wang, Y., Zhao, C. P., Liu, F., Chen, K. H., & Ran, H. (2014). Research on relationship between geochemical characteristics of thermal springs and seismic activity in Xiaojiang fault zone and its adjacent area. Journal of Seismological Research (in Chinese), 37, 228–243.
Wang, Q., Gao, Y., & Shi, Y. T. (2015). Rayleigh wave azimuthal anisotropy on the southeastern front of the Tibetan Plateau from seismic ambient noise. Chinese Journal of Geophysics (in Chinese), 58(11), 4068–4078.
Wang, W., Wu, J., & Fang, L. (2017). Crustal thickness and Poisson’s ratio in Southwest China based on data from dense seismic array. Journal of Geophysical Reasearch, 122, 7219–7235.
Wang, W., Wu, J. P., & Hammond, J. O. S. (2021). Mantle dynamics beneath the Sichuan Basin and eastern Tibet from teleseismic tomography. Tectonics, 40, 6319. https://doi.org/10.1029/2020TC006319
Wei, W., Sun, R. M., & Shi, Y. P. (2010). P-wave tomographic images beneath southeastern Tibet: Investigating the mechanism of the 2008 Wenchuan earthquake. Science in China Series D-Earth Sciences (in Chinese), 40(7), 831–839. https://doi.org/10.1360/zd2010-40-7-831
Wei, Z. Y., He, H. L., Shi, F., Xu, Y. R., Bi, L. S., & Sun, H. Y. (2012). Slip rate on the south segment of Daliangshan fault zone. Seismology and Geology (in Chinese), 34(2), 282–293.
Wen, X. Z., & Bai, L. X. (1985). Study on the deformation composition and the motion feature of the Xianshuihe active fault zone. Earthquake Research in China, 1(4), 53–59.
Wen, X. Z., Du, P. S., & Long, D. X. (2000). New evidence of paleoearthquakes and date of the latest event on the Xiaoxiangling Mountain segment of the Anninghe fault zone. Seismology and Geology, 22(1), 1–8.
Wen, X. Z., Fan, J., Yi, G. X., Deng, Y. W., & Long, F. (2008a). A seismic gap on the Anninghe fault in western Sichuan, China. Science in China Series d: Earth Sciences (in Chinese), 38(7), 797–807.
Wen, X. Z., Ma, S. L., Xu, X. W., & He, Y. N., (2008b). Historical pattern and behavior of earthquake ruptures along the eastern boundary of the Sichuan-Yunnan faulted-block, southwestern China. Physics of the Earth and Planetary Interiors, 168(1–2), 16–36.
Wen, X. Z., Du, F., Long, F., Fan, J., & Zhu, H. (2011). Tectonic dynamics and correlation of major earthquake sequences of the Xiaojiang and Qujiang-Shiping fault systems, Yunnan. China. Science China Earth Sciences (in Chinese), 54(10), 1563–1575.
Weng, H., Yang, Z., Zhang, Z., & Chen, X. F. (2016). Earthquake rupture extents and co- seismic slips promoted by damaged fault zones. Journal of Geophysical Research, 121(6), 4446–4457. https://doi.org/10.1002/2015JB012713
Willett, S., Beaumont, C., & Fullsack, P. (1993). Mechanical model for the tectonics of doubly vergent compressional orogens. Geology, 21(4), 371–374.
Wu, J. P., Yang, T., Wang, W. L., Ming, Y. H., & Zhang, T. Z. (2013). Three dimensional P-wave velocity structure around Xiaojiang fault system and its tectonic implications. Chinese Journal of Geophysics (in Chinese), 56(7), 2257–2267. https://doi.org/10.6038/cjg20130713
Xia, X., Li, Z. W., Bao, F., Xie, J., Shi, Y. T., You, Q. Y., & Chen, H. P. (2021). Sedimentary structure of the Sichuan Basin derived from seismic ambient noise tomography. Geophysical Journal International, 225, 54–67.
Xie, J., Ritzwoller, M. H., Shen, W. S., Yang, Y. J., Zheng, Z., & Zhou, L. Q. (2013). Crustal radial anisotropy across Eastern Tibet and the Western Yangtze Craton. Journal of Geophysical Research: Solid Earth, 118, 4226–4252.
Xie, J. Y., Ritzwoller, M. H., Shen, W. S., & Wang, W. T. (2017). Crustal anisotropy across eastern Tibet and surroundings modeled as a depth-dependent tilted hexagonally symmetric medium. Geophysical Journal International, 209(1), 466–491.
Xu, G. Q., & Kamp, P. J. J. (2000). Tectonics and denudation adjacent to the Xianshuihe Fault, eastern Tibetan Plateau: Constraints from fission track thermochronology. Journal of Geophysical Research, 105(B8), 19231–19251.
Xu, Z. Q., Jiang, M., & Yang, J. S. (1999). Mantle diapir inward intracontinental subduction: A discuss on the mechanism of uplift of the Qinghai-Tibet plateau. Geological Society of America, Special Paper, 328, 19–31.
Xu, X. W., Zhang, P. Z., Wen, X. Z., Qin, Z. L., Chen, G. H., & Zhu, A. L. (2005). Features of active tectonics and recurrence behaviors of strong earthquakes in the western Sichuan Province and its adjacent regions. Seismology and Geology (in Chinese), 27(3), 446–461.
Xu, Z. Q., Li, H. Q., Fu, X. F., Chen, W., Zeng, L. S., Cai, Z. H., & Chen, F. Y. (2007). Uplift of the Longmen-Jinping orogenic belt along the eastern margin of the Qinghai-Tibet Plateau: Large-scale detachment faulting and extrusion mechanism. Geological Bulletin of China (in Chinese), 26(10), 1262–1276.
Xu, M., Zhu, C. Q., Tian, Y. T., Rao, S., & Hu, S. B. (2011). Borehole temperature logging and characteristics of subsurface temperature in the Sichuan Basin. Chinese Journal of Geophysics (in Chinese), 54(4), 1052–1060.
Xu, Y., Yang, X. T., & Liu, J. H., (2013). Tomographic study of crustal velocity structures in the Yunnan region southwest China. Chinese Journal of Geophysics (in Chinese), 56(6), 1904–1914.
Yang, Y. J., Ritzwoller, M. H., Levshin, A. L., & Shapiro, N. M. (2007). Ambient noise Rayleigh wave tomography across Europe. Geophysical Journal International, 168, 259–274. https://doi.org/10.1111/j.1365-246X.2006.03203.x
Yang, T., Wu, J. P., Fang, L. H., & Wang, W. L. (2014). Complex structure beneath the Southeastern Tibetan Plateau from Teleseismic P-Wave Tomography. Bulletin of the Seismological Society of America, 104(3), 1056–1069.
Yang, H. F., Duan, Y. H., Song, J. H., Jiang, X. H., Tian, X. F., Yang, W., Wang, W. T., & Yang, J. (2020). Fine structure of the Chenghai Fault Zone, Yunnan, China, constrained from teleseismic travel time and ambient noise tomography. Journal of Geophysical Research: Solid Earth, 125, e2020JB019565. https://doi.org/10.1029/2020JB019565
Yao, H. J., Xu, G. M., Xiao, X., & Zhu, L. B. (2004). A quick tracing method based on image analysis technique for the determination of dual stations phase dispersion curve of surface wave. Seismological and Geomagnetic Observation and Research (in Chinese), 25(1), 1–8.
Yao, H. J., Xu, G. M., & Zhu, L. B. (2005). Mantle structure from inter-station Rayleigh wave dispersion and its tectonic implication in western China and neighboring regions. Physics of the Earth and Planetary Interiors, 148(1), 39–54.
Yao, H. J., Van der Hilst, R. D., & de Hoop, M. V. (2006). Surface-wave array tomography in SE Tibet from ambient seismic noise and two-station analysis - I. Phase Velocity Maps. Geophysical Journal International, 166, 732–744.
Yao, H. J., Beghein, C., & van der Hilst, R. D. (2008). Surface wave array tomography in SE Tibet from ambient seismic noise and two-station analysis – II. Crustal and upper-mantle structure. Geophysical Journal International, 173(1), 205–219.
Yao, H. J., Van der Hilst, R. D., & Montagner, J. P. (2010). Heterogeneity and anisotropy of the lithosphere of SE Tibet from surface wave array tomography. Journal of Geophysical Research Solid Earth. https://doi.org/10.1029/2009JB007142
Yao, H. J., Gouédard, P., Collins, J. A., McGuire, J. J., & van det Hilst, R. D. (2011). Structure of young East Pacific Rise lithosphere from ambient noise correlation analysis of fundamental-and higher-mode Scholte-Rayleigh waves. Comptes Rendus Geoscience, 343(8–9), 571–583.
Yi, G. X., Wen, X. Z., Fan, J., & Wang, S. W. (2004). Assessing current faulting behaviors and seismic risk of the Anninghe-Zemuhe fault zone from seismicity parameters. Acta Seismologica Sinica (in Chinese), 26(3), 294–303.
Yi, G. X., Fan, J., & Wen, X. Z. (2005). Study on faulting behavior and fault-segments for potential strong earthquake risk along the central-southern segment of Xianshuihe fault zone based on current seismicity. Earthquake (in Chinese), 25(1), 58–66.
Yi, G. X., Wen, X. Z., & Su, Y. J. (2008). Study on the potential strong-earthquake risk for the eastern boundary of the Sichuan-Yunan active faulted-block. China. Chinese Journal of Geophysics (in Chinese), 51(6), 1719–1725.
Yi, G. X., Yao, H. J., Zhu, J. S., & van der Hilst, R. D. (2010). Lithospheric deformation of continental China from Rayleigh wave azimuthal anisotropy. Chinese Journal of Geophysics (in Chinese), 53(2), 256–268.
Yu, N., Wang, X. B., Li, D. W., Li, X., Wang, E. C., Kong, W. X., & Li, T. Y. (2022). The mechanism of deep material transport and seismogenic environment of the Xiaojiang fault system revealed by 3-D magnetotelluric study. Science China Earth Sciences (in Chinese), 65(6), 1128–1145. https://doi.org/10.1007/s11430-021-9914-3
Zhang, P. Z. (2013). A review on active tectonics and deep crustal processes of the Western Sichuan region, eastern margin of the Tibetan Plateau. Tectonophysics, 584, 7–22.
Zhang, J., & Langston, C. A. (2020). Separating the scattered wavefield from teleseismic P using curvelets on the long beach array data set. Geophysical Journal International, 220(2), 1112–1127.
Zhang, Y. X., Luo, Y. N., & Yang, C. X. (1988). The Panxi Tift. Geological Press. (in Chinese).
Zhang, P. Z., Shen, Z. K., Wang, M., Gan, W. J., Bürgmann, R., Molnar, P., Wang, Q., Niu, Z. J., Sun, J. Z., Wu, J. C., Sun, H. R., & You, X. Z. (2004a). Continuous deformation of the Tibetan Plateau from global positioning system data. Geology, 32(9), 809–812. https://doi.org/10.1130/G20554.1
Zhang, Y. Q., Chen, W., & Yang, N. (2004b). 40Ar/39Ar dating of shear deformation of the Xianshuihe fault zone in west Sichuan and its tectonic significance. Science in China Series D Earth Sciences (in Chinese), 47(9), 794–803.
Zhang, Y. Y., Yao, H. J., Yang, H. Y., Cai, H. T., Fang, H. J., Xu, J. J., Jin, X., Chen, H. K., Liang, W. T., & Chen, K. X. (2018). 3-D Crustal Shear-Wave Velocity Structure of the Taiwan Strait and Fujian, SE China, Revealed by Ambient Noise Tomography. Journal of Geophysical Research: Solid Earth, 123(9), 8016–8031.
Zhang, Z. Q., Yao, H. J., & Yang, Y. (2020). Shear wave velocity structure of the crust and upper mantle in Southeastern Tibet and its geodynamic implications. Science China Earth Sciences. https://doi.org/10.1007/s11430-020-9625-3
Zhao, L. F., Xie, X. B., He, J. K., Tian, X., & Yao, Z. X. (2013). Crustal flow pattern beneath the Tibetan Plateau constrained by regional Lg-wave Q tomography. Earth and Planetary Science Letters, 383, 113–122.
Zhao, J., Jiang, Z. S., Niu, A. F., Liu, J., Wu, Y. Q., Wei, W. X., Liu, X. X., & Yan, W. (2015). Study on dynamic characteristics of fault locking and fault slip deficit in the eastern boundary of the Sichuan-Yunnan rhombic block. Chinese Journal of Geophysics (in Chinese), 58(3), 872–885.
Zheng, C., Ding, Z. F., & Song, X. D. (2016). Joint inversion of surface wave dispersion and receiver functions for crustal and uppermost mantle structure in Southeast Tibetan Plateua. Chinese Journal of Geophysics (in Chinese), 59(9), 3223–3236.
Zhou, M. F., Robinson, P. T., Lesher, C. M., Keays, R. R., Zhang, C. J., & Malpas, J. (2005). Geochemistry, petrogenesis and metallogenesis of the Panzhihua gabbroic layered intrusion and associated Fe-Ti-V oxide deposits, Sichuan province, SW China. Journal of Petrology, 46(11), 2253–2280.
Zhu, J. S., Wang, X. B., Yang, Y. H., Fan, J., & Cheng, X. Q. (2017). The crustal flow beneath the eastern margin of the Tibetan Plateau and its process of dynamics. Chinese Journal of Geophysics, 60(6), 2038–2057
Acknowledgements
We appreciate two reviewers and Prof. Yangfan Deng for their constructive comments and suggestions. We thank Prof. Weilai Wang for preparing the waveform data and Dr. Zhiqi Zhang for providing the velocity model for comparison. This study was funded by the National Natural Science Foundation of China (U2139205) project and the Special Fund for Basic Research Operations of the Institute of Geophysics, China Earthquake Administration (DQJB22X08). Figures were plotted using GMT and MATLAB.
Funding
This work was supported by the National Natural Science Foundation of China, U2139205 and the Special Fund for Basic Research Operations of the Institute of Geophysics, China Earthquake Administration, DQJB22X08.
Author information
Authors and Affiliations
Contributions
Data collection, process and analysis were performed by YQ, JL, LF, ZL and GC. The manuscript was written by YQ and SW. LF made suggestions on data process and interpretation. LF reviewed and modified the manuscript. All authors commented on previous versions of the manuscript and read and approved the final manuscript.
Corresponding author
Ethics declarations
Conflict of Interest
The authors have no relevant financial or non-financial interests to disclose.
Additional information
Publisher's Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Qiu, Y., Fang, L., Liu, J. et al. Two Unconnected Low-Velocity Zones in the Eastern Boundary of the Sichuan-Yunnan Block Revealed with High-Resolution Ambient Noise Tomography. Pure Appl. Geophys. 180, 1015–1035 (2023). https://doi.org/10.1007/s00024-023-03245-7
Received:
Revised:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s00024-023-03245-7