Crustal seismic imaging of Northeast Tibet using first and later phases of earthquakes and explosions

Sun, Anhui; Zhao, Dapeng; Gao, Yuan; Qinjian, Tian; Liu, Ning

doi:10.1093/gji/ggz031

Cited by 3 publications

(10 citation statements)

References 81 publications

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“…Thus, adding the PmP data can effectively improve crisscrossing and coverage of ray paths in the whole crust, especially in the middle to lower crust. This was also found by previous tomographic studies (Lei et al, 2008; Sun et al, 2008, 2019; Wang et al, 2018; Xia et al, 2007; D. Zhao et al, 2005).…”

Section: Methodssupporting

confidence: 86%

“…These long Pn wave data are also used in the earthquake relocation. As a result, the RMS traveltime residual of the Pn data is reduced significantly from 0.546 s in Sun et al (2019) to 0.413 s in this study.…”

Section: Methodscontrasting

confidence: 40%

“…The global crustal model LITHO1.0 was created by fitting surface wave dispersion data over a wide frequency band and updated based on a new database of crustal 1‐D profiles from active‐source seismic soundings and receiver function studies (Pasyanos et al, 2014). Sun et al (2019) derived an optimal 1‐D crustal Vp model with three undulated velocity discontinuities for NE Tibet from the LITHO1.0 model. Because the refracted Pn phase and the reflected PmP phase are sensitive to the Moho depth (Hearn et al, 2019), Sun et al (2019) found that the average crustal thickness in the initial model (50.9 km) is generally consistent with results of deep seismic sounding (J. Zhao et al, 2005) and receiver functions (Liu et al, 2017; Wang et al, 2016) in NE Tibet, which is much deeper than the Moho depth (35 km) in the IASP91 model (Kennett & Engdahl, 1991) and the AK135 model (Kennett, 2005) used by many previous tomographic studies of NE Tibet.…”

Section: Methodsmentioning

confidence: 99%

“…Four grid meshes are arranged at depths of 5, 15, 30, and 60 km. To better constrain the uppermost mantle structure beneath NE Tibet, we have improved the 3‐D ray tracing and earthquake relocation, as compared with those in Sun et al (2019). We have also used the Pn wave data with long epicentral distances and allowed the long Pn rays to dive into the upper mantle (Figure 2) rather than restricting the Pn rays directly below the Moho discontinuity.…”

Section: Methodsmentioning

confidence: 99%

“…The delay time for the crustal anisotropy measured by Pms splitting (Shen et al, 2015; Xu et al, 2018) is generally <0.7 s, whereas the delay times inferred from local earthquakes in the upper crust are <0.1 s beneath NE Tibet (Qian et al, 2017). Widespread low‐velocity (low‐V) zones are revealed in the middle to lower crust beneath NE Tibet (Li et al, 2014; Sun et al, 2019; Tian et al, 2014; Wang et al, 2008; Zhang et al, 2011), which may greatly contribute to crustal anisotropy (Kong et al, 2016). Hence, to clarify the role of the low‐V zones in the current deformation and evolution of the crust beneath NE Tibet, we need more detailed information on the three‐dimensional (3‐D) structure and dynamics in the middle to lower crust.…”

Section: Introductionmentioning

confidence: 99%

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Anisotropic Tomography Beneath Northeast Tibet: Evidence for Regional Crustal Flow

Sun

Zhao

2020

Tectonics

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We present high‐resolution tomographic images of isotropic P wave velocity and azimuthal anisotropy in the crust and uppermost mantle beneath NE Tibet by jointly inverting 62,339 arrival times of the first P and later PmP waves from 6,602 local earthquakes and 9 seismic explosions. Widespread low‐velocity zones in the middle crust contribute most of seismic anisotropy in the crust beneath NE Tibet. The predominant fast‐velocity directions of azimuthal anisotropy are closely correlated with the stress field revealed by GPS observations and focal mechanism solutions in the transition zones among the Alxa block, the Ordos basin, and the Tibetan Plateau. We attribute this feature to regional crustal flow that has intruded northeastward into NE Tibet and possibly affected vertical ground motions, whereas the flow has been resisted by the surrounding rigid blocks and so failed to further extrude eastward between the Ordos basin and the Sichuan basin. The crustal flow is responsible for the intracrust and crust‐mantle decoupling beneath the transition zones of NE Tibet. High‐velocity zones with depth‐consistent anisotropy are found to border the southwestern Ordos basin between 105° and 106°E. The rigid blocks, major active faults (e.g., the Haiyuan, Qinling, and Kunlun faults), and their interactions cause the regional tectonic features and seismic activities. Accommodation of the different deformation patterns and the tectonic interactions may explain the complicated geodynamic evolution of the crust beneath NE Tibet.

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Section: Methodssupporting

confidence: 86%

Section: Methodscontrasting

confidence: 40%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Anisotropic Tomography Beneath Northeast Tibet: Evidence for Regional Crustal Flow

Sun

Zhao

2020

Tectonics

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Elongated Magma Plumbing System Beneath the Coso Volcanic Field, California, Constrained by Seismic Reflection Tomography

Wang

et al. 2022

JGR Solid Earth

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The Coso volcanic field (CVF) is situated in a tectonically complex region in southern California, bounded by the Basin and Range in the east, the Sierra Nevada block in the west, the Owens Valley in the north, and the Garlock Fault in the south (Figure 1). The CVF is well-known for its compositionally bimodal Pleistocene magmatism, represented by the coexistence of high-silica rhyolite and basalts erupted at a constant rate during the past ∼0.5 Ma (e.g., Bacon, 1982;Manley & Bacon, 2000). The evolution of the CVF is closely related to a releasing bend between the Airport Lake Fault and the Owens Valley Fault, which was developed following the earlier extensional regime introduced by the westward propagating Basin and Range extension (e.g., Duffield et al., 1980;McQuarrie & Oskin, 2010;Monastero et al., 2005). The present-day transtensional deformation results in widely distributed crustal shearing and strike-slip faulting of the brittle upper crust, leading to intensive earthquake activities in this region (Monastero et al., 2005).Geochemical and thermobarometric studies indicate the existence of a long-lasting magma reservoir beneath the CVF in the upper to middle crust, which directly feeds the Pleistocene volcanic activities and supplies the

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Anisotropic tomography of eastern Tibet and its uncertainty from hypocentral errors

Jia,

Zhao,

2024

Geophysical Journal International

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Summary The mechanism responsible for the lateral expansion and uplift of the eastern Tibetan Plateau remains a topic of ongoing debate, partly due to discrepancies in the results of seismic velocity and anisotropy. In local earthquake tomography, hypocentral uncertainties can cause significant errors in the tomographic model. However, this issue has received limited attention in previous studies. In this work, we employ the weighted least-squares (WLS) method to solve the tomographic inversion problem. A power exponent coefficient, which is called weighting level, is introduced into the weighting matrix to control the relative contribution of the data with different hypocentral errors to the final tomographic result. Our data set contains high-quality Pg, Pn and Sg arrival times of local earthquakes recorded by the dense Chinese seismic network in eastern Tibet during 2008 to 2022. We comprehensively analyze the inversion results derived from the WLS inversions with different weighting levels to evaluate the robustness of isotropic velocity anomalies and azimuthal anisotropy. The most robust feature of our results is a striking low-velocity (low-Vp) zone surrounded by high-velocity (high-Vp) anomalies and fault parallel fast-velocity directions (FVDs) of azimuthal anisotropy in the lower crust beneath the western side of the Longmenshan fault zone. Taking into account many previous results of the region, we deem that the low-Vp zone reflects hot and wet upwelling flow from the deep asthenosphere, which ascends to the lower crust along the fault zone. At the NE margin of the Tibetan Plateau, significant low-Vp anomalies exist in the lower crust and the FVDs are consistent with the motion direction of the Tibetan block revealed by GPS observations. We think that lower crustal flow exists beneath NE Tibet, which controls the plateau expansion toward the northeast. A low-Vp anomaly appears at 30 km depth beneath the Sichuan Basin. However, as the weighting level increases, the amplitude of this low-Vp anomaly decreases by more than 6%, suggesting that this low-Vp anomaly has a larger uncertainty than the other features.

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Crustal seismic imaging of Northeast Tibet using first and later phases of earthquakes and explosions

Cited by 3 publications

References 81 publications

Anisotropic Tomography Beneath Northeast Tibet: Evidence for Regional Crustal Flow

Anisotropic Tomography Beneath Northeast Tibet: Evidence for Regional Crustal Flow

Elongated Magma Plumbing System Beneath the Coso Volcanic Field, California, Constrained by Seismic Reflection Tomography

Anisotropic tomography of eastern Tibet and its uncertainty from hypocentral errors

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