Journal of Geophysical Research: Solid Earth, 2019
The SE Tibetan Plateau is located between the eastern Himalayan syntaxis and the stable Yangtze c... more The SE Tibetan Plateau is located between the eastern Himalayan syntaxis and the stable Yangtze craton; its tectonic evolution is important for understanding the plateau expansion. However, interactions between the plateau and its adjacent subduction zone and craton are still unclear. In this study, we determine updated high‐resolution P and S wave tomographic models of the crust and upper mantle beneath the SE Tibetan Plateau. We confirmed the existence of a high‐velocity layer in the upper mantle down to 200‐km depth beneath the Sichuan basin, the core of the Yangtze craton, representing the stable cratonic root. Another high‐velocity body is located beneath Burma, reflecting the subducting Indian slab in the upper mantle and possibly the remnant Burman slab in the mantle transition zone. A strong low‐velocity column exists above the high‐velocity body in the transition zone and reaches the Moho under the Tengchong volcano. In addition, we find high‐velocity fragments in the upper...
The mechanism and pattern of deformation beneath western Tibet are still an issue of debate. In t... more The mechanism and pattern of deformation beneath western Tibet are still an issue of debate. In this work we present 3-D P-and S-wave velocity tomography as well as P-wave radial and azimuth anisotropy along the ANTILOPE-I profile and surrounding areas in western Tibet, which are determined by using a large number of P and S arrival-time data of local earthquakes and teleseismic events. Our result show that low-velocity (low-V) zones exist widely in the middle crust, whereas low-V zones are only visible in the lower crust beneath northwestern Tibet, indicating the existence of significant heterogeneities and complex flow there. In the upper mantle, a distinct
In order to better understand the deep structure and dynamics of the Earth's interior, we have at... more In order to better understand the deep structure and dynamics of the Earth's interior, we have attempted to develop a new model of whole mantle seismic tomography with a novel approach. We adopted a grid parameterization instead of blocks which were used in most of the global tomographic studies. Ray paths and travel times are computed with an efficient 3-D ray tracing scheme. Moreover, the topography of mantle discontinuities at 410 and 660 km depths are taken into account in the tomographic inversions. This new approach was applied to a large data set of ISC travel times (P, PP, PcP, pP) to determine a whole mantle P-wave tomography. For the shallow mantle, our new model contains the general features observed in the previous models : a low-velocity ring around the Pacific Ocean basins and high-velocity anomalies under the old and stable continents in the depth range of 0-400 km. One significant difference from the previous models is that stronger and wider high-velocity anomalies are visible in the transition zone depths under the subduction zone regions, which suggests that most of the slab materials are stagnant for a long time in the transition zone before finally dropping down to the lower mantle. Plume-like slow anomalies are visible under the hotspot regions in most parts of the mantle. The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, which suggests that plumes are not fixed in the mantle but can be deflected by the mantle winds. As a consequence, hotspots are not really fixed but can wander on the Earth's surface, as evidenced by the recent geomagnetic and numeric modeling studies. Wider and more prominent slow anomalies are visible at the coremantle boundary (CMB) than most of the lower mantle, and there is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, which suggest that most of the mantle plumes under the hotspots may originate from the CMB. However, there may be some small-scaled, weak plumes originating from the transition zone depths. 1.
SUMMARY We determine robust 3-D P-wave anisotropic tomography of the crust and upper mantle benea... more SUMMARY We determine robust 3-D P-wave anisotropic tomography of the crust and upper mantle beneath NE China using high-quality traveltime data of local earthquakes and teleseismic events recorded at 334 network and portable stations. In the upper crust, nearly E-W fast-velocity directions (FVDs) of azimuthal anisotropy are revealed in the central Songliao basin, which is surrounded by circular-shaped FVDs along the basin edges. The E-W FVDs may reflect microcracks or fractures in the upper crust, which are aligned under the control of regional tectonic stress. In the lower crust, low-velocity (low-V) anomalies with NE-SW FVDs exist along the Tanlu fault zone, which may reflect NE-SW trending ductile deformation or viscous flow along the fault zone. The FVDs are mainly NNW-SSE to N-S in the uppermost mantle beneath most of the study region, which may reflect fossil deformation of the mantle lithosphere caused by the Palaeo-Pacific plate subduction. High-velocity anomalies with NE-SW...
SUMMARYWe determine a new 3-D shear wave velocity (Vs) model down to 400 km depth beneath the Cap... more SUMMARYWe determine a new 3-D shear wave velocity (Vs) model down to 400 km depth beneath the Cape Verde hotspot that is far from plate boundaries. This Vs model is obtained by using a new method of jointly inverting P- and S-wave receiver functions, Rayleigh-wave phase-velocity data and S-wave arrival times of teleseismic events. Two Vs discontinuities at ∼15 and ∼60 km depths are revealed beneath volcanic islands, which are interpreted as the Moho discontinuity and the Gutenberg (G) discontinuity. Between the north and south islands, obvious high-Vs anomalies exist in the uppermost mantle down to a depth of ∼100–150 km beneath the Atlantic Ocean, whereas obvious low-Vs anomalies exist in the uppermost mantle beneath the volcanic islands including the active Fogo volcano. These low-Vs anomalies merge into a significant column-like low-Vs zone at depths of ∼150–400 km beneath the Cape Verde swell. We propose that these features in the upper mantle reflect a plume-modified oceanic li...
We investigate the 3-D seismic structure of source areas of the 6 October 2000 Western Tottori ea... more We investigate the 3-D seismic structure of source areas of the 6 October 2000 Western Tottori earthquake (M 7.3) and the 21 October 2016 Central Tottori earthquake (M 6.6) which occurred near the Daisen volcano in SW Japan. The two large events took place in a high-velocity zone in the upper crust, whereas low-velocity (low-V) and high Poisson's ratio (high-σ) anomalies are revealed in the lower crust and upper mantle. Low-frequency micro-earthquakes (M 0.0-2.1) occur in or around the low-V and high-σ zones, which reflect upward migration of magmatic fluids from the upper mantle to the crust under the Daisen volcano. The nucleation of the Tottori earthquakes may be affected by the ascending fluids. The flat subducting Philippine Sea (PHS) slab has a younger lithosphere age and so a higher temperature beneath the Daisen and Tottori area, facilitating the PHS slab melting. It is also possible that a PHS slab window has formed along the extinct Shikoku Basin spreading ridge beneath SW Japan, and mantle materials below the PHS slab may ascend to the shallow area through the slab window. These results suggest that the Daisen adakite magma was affected by the PHS slab melting and upwelling flow in the upper mantle above the subducting Pacific slab.
A new crustal 3-D P-wave velocity model beneath NE Tibet is determined by jointly inverting 62 33... more A new crustal 3-D P-wave velocity model beneath NE Tibet is determined by jointly inverting 62 339 high-quality first P wave and later PmP-wave arrival-time data from local earthquakes and seismic explosions. Resolution tests show that the use of the PmP data can effectively improve the resolution of crustal tomography, especially that of the middle-lower crust. Widespread but intermittent low-velocity anomalies are revealed in the lower crust beneath NE Tibet, and the Kunlun fault acts as a transfer structure. High-velocity zones are visible in most parts of the crust below the transition zones bordering the southwestern Ordos basin between 105 • and 106 • E longitude. We think that they form an important transpressive boundary to absorb sinistral strike-slip and thrust faulting deformation, like a western frontline of the Ordos basin, which is compatible with the latest GPS observations in the region. Considering the tectonic features and deformation of the Liupanshan fault, we need to pay much attention to the seismic risk of the fault zone from now. Our results reveal different structural features of the major blocks and their boundary faults, indicating the complexity of the Cenozoic crustal deformation in NE Tibet that partitioned between steep strike-slip shear zones and thrust faults.
The great 2011 Tohoku-oki earthquake [moment magnitude () 9.0)] is the best-documented megathrust... more The great 2011 Tohoku-oki earthquake [moment magnitude () 9.0)] is the best-documented megathrust earthquake in the world, but its causal mechanism is still in controversy because of the poor state of knowledge on the nature of the megathrust zone. We constrain the structure of the Tohoku forearc using seismic tomography, residual topography, and gravity data, which reveal a close relationship between structural heterogeneities in and around the megathrust zone and rupture processes of the 2011 Tohoku-oki earthquake. Its mainshock nucleated in an area with high seismic velocity, low seismic attenuation, and strong seismic coupling, probably indicating a large asperity (or a cluster of asperities) in the megathrust zone. Strong coseismic high-frequency radiations also occurred in high-velocity patches, whereas large afterslips took plate in low-velocity areas, differences that may reflect changes in fault friction and lithological variations. These structural heterogeneities in and a...
SUMMARY An important element of seismic tomography is the inversion process. In this work, we use... more SUMMARY An important element of seismic tomography is the inversion process. In this work, we use P-wave arrival times of local earthquakes recorded at onshore and offshore seismic stations in East Japan to investigate the influence of two well-known inversion algorithms (LSQR and L-BFGS-B) on anisotropic tomography. Our synthetic tests show that a large damping parameter in the LSQR algorithm can lead to a stable and fast convergence, but it can result in many small value disturbances. The L-BFGS-B algorithm, which has second-order convergence, could converge fast to the optimal solution without damping regularization, but an inappropriate bound on the unknown parameters makes them hard to be recovered fully and causes strong trade-off between isotropic velocity and azimuthal anisotropy. If appropriate control parameters are adopted, the two inversion algorithms lead to almost the same results, though the L-BFGS-B provides a more efficient convergence and leads to a slightly better...
Inland crustal earthquakes usually occur in the brittle upper crust (0–20 km depths), but the 6 S... more Inland crustal earthquakes usually occur in the brittle upper crust (0–20 km depths), but the 6 September 2018 Eastern Iburi earthquake (M 6.7) took place in southern Hokkaido with a focal depth of ~37 km, causing 41 fatalities and serious damage to the local infrastructure. The reason why this event was so deep and its causal mechanism are still unclear. In this work we study the three-dimensional P and S wave seismic attenuation (1/Q) structure in the source zone of the 2018 Iburi earthquake. Our results show that this event occurred at the boundary between the Sorachi-Yezo belt (low Q) and the dipping Northeastern (NE) Japan arc (high Q) that is descending beneath the Kuril arc. The collision between the NE Japan and Kuril arcs as well as fluids from dehydration of the subducting Pacific plate caused this big event and its unusual focal depth. Similar attenuation structures are revealed in source zones of the 1970 Hidaka earthquake (M 6.7) and the 1982 Urakawa-oki earthquake (M 7...
Seismic anisotropy tomography is the updated geophysical imaging technology that can reveal 3-D v... more Seismic anisotropy tomography is the updated geophysical imaging technology that can reveal 3-D variations of both structural heterogeneity and seismic anisotropy, providing unique constraints on geodynamic processes in the Earth’s crust and mantle. Here we introduce recent advances in the theory and application of seismic anisotropy tomography, thanks to abundant and high-quality data sets recorded by dense seismic networks deployed in many regions in the past decades. Applications of the novel techniques led to new discoveries in the 3-D structure and dynamics of subduction zones and continental regions. The most significant findings are constraints on seismic anisotropy in the subducting slabs. Fast-velocity directions (FVDs) of azimuthal anisotropy in the slabs are generally trench-parallel, reflecting fossil lattice-preferred orientation of aligned anisotropic minerals and/or shape-preferred orientation due to transform faults produced at the mid-ocean ridge and intraslab hydra...
High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi... more High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60-100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.
The mechanism and rupture process of the giant 2011 Tohoku-oki earthquake (Mw 9.0) are still poor... more The mechanism and rupture process of the giant 2011 Tohoku-oki earthquake (Mw 9.0) are still poorly understood due to lack of permanent near-field observations. Using seismic arrival times recorded by dense seismograph networks on land and at ocean floor, we determine a detailed seismic tomography model of the megathrust zone beneath the Tohoku forearc. Our results show that the coseismic slip of the 2011 Tohoku-oki earthquake initiated at a boundary between a down-dip high-velocity anomaly and an up-dip low-velocity anomaly. The slow anomaly at shallow depths near the Japan trench may reflect low-rigidity materials that are close to the free surface, resulting in large slip and weak high-frequency radiation. Our new tomographic model can account for not only large slip near the trench but also weak high-frequency radiation from the shallow rupture areas.
Detailed three-dimensional images of P and S wave velocity and Poisson's ratio (σ) of the crust a... more Detailed three-dimensional images of P and S wave velocity and Poisson's ratio (σ) of the crust and upper mantle beneath Kyushu in SW Japan are determined, with a focus on the source area of the 2016 Kumamoto earthquake (M 7.3) that occurred in the Beppu-Shimabara graben (BSG) where four active volcanoes and many active faults exist. The 2016 Kumamoto earthquake took place in a high-velocity and low-σ zone in the upper crust, which is surrounded and underlain by low-velocity and high-σ anomalies in the upper mantle. This result suggests that, in and around the source zone of the 2016 Kumamoto earthquake, strong structural heterogeneities relating to active volcanoes and magmatic fluids exist, which may affect the seismogenesis. Along the BSG, low-velocity and high-σ anomalies do not exist everywhere in the upper mantle but mainly beneath the active volcanoes, suggesting that hot mantle upwelling is not the only cause of the graben. The BSG was most likely formed by joint effects of northward extension of the Okinawa Trough, westward extension of the Median Tectonic Line, and hot upwelling flow in the mantle wedge beneath the active volcanoes.
We relocated the great 2011 Tohoku-oki earthquake (Mw 9.0) and its foreshocks and aftershocks usi... more We relocated the great 2011 Tohoku-oki earthquake (Mw 9.0) and its foreshocks and aftershocks using a three-dimensional seismic velocity model and high-quality P and S wave arrival times recorded by the dense seismic network on the Japan Islands. Then we compared the distribution of the relocated hypocenters with a high-resolution tomographic image of the Northeast Japan forearc. The comparison indicates that the rupture nucleation of the largest events in the Tohoku-oki sequence, including the mainshock, was controlled by structural heterogeneities in the interplate megathrust zone.
The 2016 Kumamoto earthquake (M 7.3 in the Japan Meteorological Agency (JMA) scale) sequence wrot... more The 2016 Kumamoto earthquake (M 7.3 in the Japan Meteorological Agency (JMA) scale) sequence wrote a new chapter of active seismotectonics and subduction dynamics in the Japan Islands. This earthquake sequence, taking place in the upper crust beneath Kyushu Island (Fig. 1), began with a strong foreshock (M 6.5) at local time 21:26 on 14 April 2016 and another big foreshock (M 6.4) at 00:03 on 15 April in the central part of Kumamoto Prefecture. Its main shock (M 7.3) occurred at 01:25 on 16 April in the vicinity of the two foreshocks (Fig. 2a, b), which was followed by thousands of aftershocks (M 1.0-5.9) by 25 April (Fig. 1), according to the JMA reports (http://www.jma.go.jp). The Kumamoto earthquakes were caused by ruptures of the Futagawa and Hinagu fault zones which are the representative faults in Kyushu. This earthquake sequence has extended toward the southwest and the northeast, reaching Ooita Prefecture in Northeast Kyushu (Fig. 1), indicating that most of the Bepu-Shimabara rift zone across Kyushu has been activated which is composed of numerous active faults and several active arc volcanoes such as Aso, Kuju and Tsurumi-dake (Figs. 1, 2). The closest volcano to the main shock, Aso, has been more active before and after the Kumamoto earthquake, suggesting that the volcano and the
SUMMARY Cenozoic basalts with ages ranging from 28.5 to < 0.1 Ma are widely distributed in the... more SUMMARY Cenozoic basalts with ages ranging from 28.5 to < 0.1 Ma are widely distributed in the Indochina block, the South China Sea basin and the Leiqiong area in South China including the Leizhou Peninsula and the northern Hainan Island, which form the southeastern Asian basalt province (SABP). These Cenozoic basalts share common petrological and geochemical characteristics. However, the origin of the Cenozoic intraplate volcanism in the SABP is still a controversial issue. In this work, we apply a novel technique of multiscale global tomography to study the whole-mantle 3-D P-wave velocity (Vp) structure beneath the SABP. Our results show that low-Vp anomalies prevail in the whole mantle beneath the SABP. Although the strongest low-Vp zones exist beneath Hainan, significant low-Vp anomalies are also visible in the mantle beneath other parts of the SABP. These low-Vp anomalies appear somehow independent, rather than deriving from a single plume. We deem that a cluster of plumes ...
Journal of Geophysical Research: Solid Earth, 2019
The SE Tibetan Plateau is located between the eastern Himalayan syntaxis and the stable Yangtze c... more The SE Tibetan Plateau is located between the eastern Himalayan syntaxis and the stable Yangtze craton; its tectonic evolution is important for understanding the plateau expansion. However, interactions between the plateau and its adjacent subduction zone and craton are still unclear. In this study, we determine updated high‐resolution P and S wave tomographic models of the crust and upper mantle beneath the SE Tibetan Plateau. We confirmed the existence of a high‐velocity layer in the upper mantle down to 200‐km depth beneath the Sichuan basin, the core of the Yangtze craton, representing the stable cratonic root. Another high‐velocity body is located beneath Burma, reflecting the subducting Indian slab in the upper mantle and possibly the remnant Burman slab in the mantle transition zone. A strong low‐velocity column exists above the high‐velocity body in the transition zone and reaches the Moho under the Tengchong volcano. In addition, we find high‐velocity fragments in the upper...
The mechanism and pattern of deformation beneath western Tibet are still an issue of debate. In t... more The mechanism and pattern of deformation beneath western Tibet are still an issue of debate. In this work we present 3-D P-and S-wave velocity tomography as well as P-wave radial and azimuth anisotropy along the ANTILOPE-I profile and surrounding areas in western Tibet, which are determined by using a large number of P and S arrival-time data of local earthquakes and teleseismic events. Our result show that low-velocity (low-V) zones exist widely in the middle crust, whereas low-V zones are only visible in the lower crust beneath northwestern Tibet, indicating the existence of significant heterogeneities and complex flow there. In the upper mantle, a distinct
In order to better understand the deep structure and dynamics of the Earth's interior, we have at... more In order to better understand the deep structure and dynamics of the Earth's interior, we have attempted to develop a new model of whole mantle seismic tomography with a novel approach. We adopted a grid parameterization instead of blocks which were used in most of the global tomographic studies. Ray paths and travel times are computed with an efficient 3-D ray tracing scheme. Moreover, the topography of mantle discontinuities at 410 and 660 km depths are taken into account in the tomographic inversions. This new approach was applied to a large data set of ISC travel times (P, PP, PcP, pP) to determine a whole mantle P-wave tomography. For the shallow mantle, our new model contains the general features observed in the previous models : a low-velocity ring around the Pacific Ocean basins and high-velocity anomalies under the old and stable continents in the depth range of 0-400 km. One significant difference from the previous models is that stronger and wider high-velocity anomalies are visible in the transition zone depths under the subduction zone regions, which suggests that most of the slab materials are stagnant for a long time in the transition zone before finally dropping down to the lower mantle. Plume-like slow anomalies are visible under the hotspot regions in most parts of the mantle. The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, which suggests that plumes are not fixed in the mantle but can be deflected by the mantle winds. As a consequence, hotspots are not really fixed but can wander on the Earth's surface, as evidenced by the recent geomagnetic and numeric modeling studies. Wider and more prominent slow anomalies are visible at the coremantle boundary (CMB) than most of the lower mantle, and there is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, which suggest that most of the mantle plumes under the hotspots may originate from the CMB. However, there may be some small-scaled, weak plumes originating from the transition zone depths. 1.
SUMMARY We determine robust 3-D P-wave anisotropic tomography of the crust and upper mantle benea... more SUMMARY We determine robust 3-D P-wave anisotropic tomography of the crust and upper mantle beneath NE China using high-quality traveltime data of local earthquakes and teleseismic events recorded at 334 network and portable stations. In the upper crust, nearly E-W fast-velocity directions (FVDs) of azimuthal anisotropy are revealed in the central Songliao basin, which is surrounded by circular-shaped FVDs along the basin edges. The E-W FVDs may reflect microcracks or fractures in the upper crust, which are aligned under the control of regional tectonic stress. In the lower crust, low-velocity (low-V) anomalies with NE-SW FVDs exist along the Tanlu fault zone, which may reflect NE-SW trending ductile deformation or viscous flow along the fault zone. The FVDs are mainly NNW-SSE to N-S in the uppermost mantle beneath most of the study region, which may reflect fossil deformation of the mantle lithosphere caused by the Palaeo-Pacific plate subduction. High-velocity anomalies with NE-SW...
SUMMARYWe determine a new 3-D shear wave velocity (Vs) model down to 400 km depth beneath the Cap... more SUMMARYWe determine a new 3-D shear wave velocity (Vs) model down to 400 km depth beneath the Cape Verde hotspot that is far from plate boundaries. This Vs model is obtained by using a new method of jointly inverting P- and S-wave receiver functions, Rayleigh-wave phase-velocity data and S-wave arrival times of teleseismic events. Two Vs discontinuities at ∼15 and ∼60 km depths are revealed beneath volcanic islands, which are interpreted as the Moho discontinuity and the Gutenberg (G) discontinuity. Between the north and south islands, obvious high-Vs anomalies exist in the uppermost mantle down to a depth of ∼100–150 km beneath the Atlantic Ocean, whereas obvious low-Vs anomalies exist in the uppermost mantle beneath the volcanic islands including the active Fogo volcano. These low-Vs anomalies merge into a significant column-like low-Vs zone at depths of ∼150–400 km beneath the Cape Verde swell. We propose that these features in the upper mantle reflect a plume-modified oceanic li...
We investigate the 3-D seismic structure of source areas of the 6 October 2000 Western Tottori ea... more We investigate the 3-D seismic structure of source areas of the 6 October 2000 Western Tottori earthquake (M 7.3) and the 21 October 2016 Central Tottori earthquake (M 6.6) which occurred near the Daisen volcano in SW Japan. The two large events took place in a high-velocity zone in the upper crust, whereas low-velocity (low-V) and high Poisson's ratio (high-σ) anomalies are revealed in the lower crust and upper mantle. Low-frequency micro-earthquakes (M 0.0-2.1) occur in or around the low-V and high-σ zones, which reflect upward migration of magmatic fluids from the upper mantle to the crust under the Daisen volcano. The nucleation of the Tottori earthquakes may be affected by the ascending fluids. The flat subducting Philippine Sea (PHS) slab has a younger lithosphere age and so a higher temperature beneath the Daisen and Tottori area, facilitating the PHS slab melting. It is also possible that a PHS slab window has formed along the extinct Shikoku Basin spreading ridge beneath SW Japan, and mantle materials below the PHS slab may ascend to the shallow area through the slab window. These results suggest that the Daisen adakite magma was affected by the PHS slab melting and upwelling flow in the upper mantle above the subducting Pacific slab.
A new crustal 3-D P-wave velocity model beneath NE Tibet is determined by jointly inverting 62 33... more A new crustal 3-D P-wave velocity model beneath NE Tibet is determined by jointly inverting 62 339 high-quality first P wave and later PmP-wave arrival-time data from local earthquakes and seismic explosions. Resolution tests show that the use of the PmP data can effectively improve the resolution of crustal tomography, especially that of the middle-lower crust. Widespread but intermittent low-velocity anomalies are revealed in the lower crust beneath NE Tibet, and the Kunlun fault acts as a transfer structure. High-velocity zones are visible in most parts of the crust below the transition zones bordering the southwestern Ordos basin between 105 • and 106 • E longitude. We think that they form an important transpressive boundary to absorb sinistral strike-slip and thrust faulting deformation, like a western frontline of the Ordos basin, which is compatible with the latest GPS observations in the region. Considering the tectonic features and deformation of the Liupanshan fault, we need to pay much attention to the seismic risk of the fault zone from now. Our results reveal different structural features of the major blocks and their boundary faults, indicating the complexity of the Cenozoic crustal deformation in NE Tibet that partitioned between steep strike-slip shear zones and thrust faults.
The great 2011 Tohoku-oki earthquake [moment magnitude () 9.0)] is the best-documented megathrust... more The great 2011 Tohoku-oki earthquake [moment magnitude () 9.0)] is the best-documented megathrust earthquake in the world, but its causal mechanism is still in controversy because of the poor state of knowledge on the nature of the megathrust zone. We constrain the structure of the Tohoku forearc using seismic tomography, residual topography, and gravity data, which reveal a close relationship between structural heterogeneities in and around the megathrust zone and rupture processes of the 2011 Tohoku-oki earthquake. Its mainshock nucleated in an area with high seismic velocity, low seismic attenuation, and strong seismic coupling, probably indicating a large asperity (or a cluster of asperities) in the megathrust zone. Strong coseismic high-frequency radiations also occurred in high-velocity patches, whereas large afterslips took plate in low-velocity areas, differences that may reflect changes in fault friction and lithological variations. These structural heterogeneities in and a...
SUMMARY An important element of seismic tomography is the inversion process. In this work, we use... more SUMMARY An important element of seismic tomography is the inversion process. In this work, we use P-wave arrival times of local earthquakes recorded at onshore and offshore seismic stations in East Japan to investigate the influence of two well-known inversion algorithms (LSQR and L-BFGS-B) on anisotropic tomography. Our synthetic tests show that a large damping parameter in the LSQR algorithm can lead to a stable and fast convergence, but it can result in many small value disturbances. The L-BFGS-B algorithm, which has second-order convergence, could converge fast to the optimal solution without damping regularization, but an inappropriate bound on the unknown parameters makes them hard to be recovered fully and causes strong trade-off between isotropic velocity and azimuthal anisotropy. If appropriate control parameters are adopted, the two inversion algorithms lead to almost the same results, though the L-BFGS-B provides a more efficient convergence and leads to a slightly better...
Inland crustal earthquakes usually occur in the brittle upper crust (0–20 km depths), but the 6 S... more Inland crustal earthquakes usually occur in the brittle upper crust (0–20 km depths), but the 6 September 2018 Eastern Iburi earthquake (M 6.7) took place in southern Hokkaido with a focal depth of ~37 km, causing 41 fatalities and serious damage to the local infrastructure. The reason why this event was so deep and its causal mechanism are still unclear. In this work we study the three-dimensional P and S wave seismic attenuation (1/Q) structure in the source zone of the 2018 Iburi earthquake. Our results show that this event occurred at the boundary between the Sorachi-Yezo belt (low Q) and the dipping Northeastern (NE) Japan arc (high Q) that is descending beneath the Kuril arc. The collision between the NE Japan and Kuril arcs as well as fluids from dehydration of the subducting Pacific plate caused this big event and its unusual focal depth. Similar attenuation structures are revealed in source zones of the 1970 Hidaka earthquake (M 6.7) and the 1982 Urakawa-oki earthquake (M 7...
Seismic anisotropy tomography is the updated geophysical imaging technology that can reveal 3-D v... more Seismic anisotropy tomography is the updated geophysical imaging technology that can reveal 3-D variations of both structural heterogeneity and seismic anisotropy, providing unique constraints on geodynamic processes in the Earth’s crust and mantle. Here we introduce recent advances in the theory and application of seismic anisotropy tomography, thanks to abundant and high-quality data sets recorded by dense seismic networks deployed in many regions in the past decades. Applications of the novel techniques led to new discoveries in the 3-D structure and dynamics of subduction zones and continental regions. The most significant findings are constraints on seismic anisotropy in the subducting slabs. Fast-velocity directions (FVDs) of azimuthal anisotropy in the slabs are generally trench-parallel, reflecting fossil lattice-preferred orientation of aligned anisotropic minerals and/or shape-preferred orientation due to transform faults produced at the mid-ocean ridge and intraslab hydra...
High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi... more High-resolution tomographic images of the crust and upper mantle beneath Harrat Al-Madinah, Saudi Arabia, are obtained by inverting high-quality arrival-time data of local earthquakes and teleseismic events recorded by newly installed borehole seismic stations to investigate the AD 1256 volcanic eruption and the 1999 seismic swarm in the study region. Our tomographic images show the existence of strong heterogeneities marked with low-velocity zones extending beneath the AD 1256 volcanic center and the 1999 seismic swarm area. The low-velocity zone coinciding with the hypocenters of the 1999 seismic swarm suggests the presence of a shallow magma reservoir that is apparently originated from a deeper source (60-100 km depths) and is possibly connected with another reservoir located further north underneath the NNW-aligned scoria cones of the AD 1256 eruption. We suggest that the 1999 seismic swarm may represent an aborted volcanic eruption and that the magmatism along the western margin of Arabia is largely attributed to the uplifting and thinning of its lithosphere by the Red Sea rifting.
The mechanism and rupture process of the giant 2011 Tohoku-oki earthquake (Mw 9.0) are still poor... more The mechanism and rupture process of the giant 2011 Tohoku-oki earthquake (Mw 9.0) are still poorly understood due to lack of permanent near-field observations. Using seismic arrival times recorded by dense seismograph networks on land and at ocean floor, we determine a detailed seismic tomography model of the megathrust zone beneath the Tohoku forearc. Our results show that the coseismic slip of the 2011 Tohoku-oki earthquake initiated at a boundary between a down-dip high-velocity anomaly and an up-dip low-velocity anomaly. The slow anomaly at shallow depths near the Japan trench may reflect low-rigidity materials that are close to the free surface, resulting in large slip and weak high-frequency radiation. Our new tomographic model can account for not only large slip near the trench but also weak high-frequency radiation from the shallow rupture areas.
Detailed three-dimensional images of P and S wave velocity and Poisson's ratio (σ) of the crust a... more Detailed three-dimensional images of P and S wave velocity and Poisson's ratio (σ) of the crust and upper mantle beneath Kyushu in SW Japan are determined, with a focus on the source area of the 2016 Kumamoto earthquake (M 7.3) that occurred in the Beppu-Shimabara graben (BSG) where four active volcanoes and many active faults exist. The 2016 Kumamoto earthquake took place in a high-velocity and low-σ zone in the upper crust, which is surrounded and underlain by low-velocity and high-σ anomalies in the upper mantle. This result suggests that, in and around the source zone of the 2016 Kumamoto earthquake, strong structural heterogeneities relating to active volcanoes and magmatic fluids exist, which may affect the seismogenesis. Along the BSG, low-velocity and high-σ anomalies do not exist everywhere in the upper mantle but mainly beneath the active volcanoes, suggesting that hot mantle upwelling is not the only cause of the graben. The BSG was most likely formed by joint effects of northward extension of the Okinawa Trough, westward extension of the Median Tectonic Line, and hot upwelling flow in the mantle wedge beneath the active volcanoes.
We relocated the great 2011 Tohoku-oki earthquake (Mw 9.0) and its foreshocks and aftershocks usi... more We relocated the great 2011 Tohoku-oki earthquake (Mw 9.0) and its foreshocks and aftershocks using a three-dimensional seismic velocity model and high-quality P and S wave arrival times recorded by the dense seismic network on the Japan Islands. Then we compared the distribution of the relocated hypocenters with a high-resolution tomographic image of the Northeast Japan forearc. The comparison indicates that the rupture nucleation of the largest events in the Tohoku-oki sequence, including the mainshock, was controlled by structural heterogeneities in the interplate megathrust zone.
The 2016 Kumamoto earthquake (M 7.3 in the Japan Meteorological Agency (JMA) scale) sequence wrot... more The 2016 Kumamoto earthquake (M 7.3 in the Japan Meteorological Agency (JMA) scale) sequence wrote a new chapter of active seismotectonics and subduction dynamics in the Japan Islands. This earthquake sequence, taking place in the upper crust beneath Kyushu Island (Fig. 1), began with a strong foreshock (M 6.5) at local time 21:26 on 14 April 2016 and another big foreshock (M 6.4) at 00:03 on 15 April in the central part of Kumamoto Prefecture. Its main shock (M 7.3) occurred at 01:25 on 16 April in the vicinity of the two foreshocks (Fig. 2a, b), which was followed by thousands of aftershocks (M 1.0-5.9) by 25 April (Fig. 1), according to the JMA reports (http://www.jma.go.jp). The Kumamoto earthquakes were caused by ruptures of the Futagawa and Hinagu fault zones which are the representative faults in Kyushu. This earthquake sequence has extended toward the southwest and the northeast, reaching Ooita Prefecture in Northeast Kyushu (Fig. 1), indicating that most of the Bepu-Shimabara rift zone across Kyushu has been activated which is composed of numerous active faults and several active arc volcanoes such as Aso, Kuju and Tsurumi-dake (Figs. 1, 2). The closest volcano to the main shock, Aso, has been more active before and after the Kumamoto earthquake, suggesting that the volcano and the
SUMMARY Cenozoic basalts with ages ranging from 28.5 to < 0.1 Ma are widely distributed in the... more SUMMARY Cenozoic basalts with ages ranging from 28.5 to < 0.1 Ma are widely distributed in the Indochina block, the South China Sea basin and the Leiqiong area in South China including the Leizhou Peninsula and the northern Hainan Island, which form the southeastern Asian basalt province (SABP). These Cenozoic basalts share common petrological and geochemical characteristics. However, the origin of the Cenozoic intraplate volcanism in the SABP is still a controversial issue. In this work, we apply a novel technique of multiscale global tomography to study the whole-mantle 3-D P-wave velocity (Vp) structure beneath the SABP. Our results show that low-Vp anomalies prevail in the whole mantle beneath the SABP. Although the strongest low-Vp zones exist beneath Hainan, significant low-Vp anomalies are also visible in the mantle beneath other parts of the SABP. These low-Vp anomalies appear somehow independent, rather than deriving from a single plume. We deem that a cluster of plumes ...
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Papers by Dapeng Zhao