This paper presents a study of global Rayleigh wave attenuation and group velocity at a period of around 20 s using data from the International Seismological Centre (ISC) bulletin. Rayleigh waves at this period are sensitive to the crustal structure beneath continents and the uppermost mantle beneath oceans. Tomographic imaging reveals strong continental-ocean contrasts due to this. Oceanic group velocities are high but vary with seafloor depth, while oceanic attenuation shows mid-ocean ridges. Subduction zone regions display high attenuation but little velocity reduction, indicating scattering attenuation. Low attenuation regions are associated with the Earth’s major cratonic regions, but there are no associated velocity changes. This implies that intrinsic attenuation is low and scattering dominates. Cratonic crustal scatterers have been annealed. A new surface wave magnitude scale is constructed that is valid from near-source to near-antipode distances.

The extremely oblique Indo-Burma subduction zone exhibits dextral strike-slip faulting along the Sagaing, Kabaw, and Churachandpur-Mao Faults as well as east-west shortening between the Sagaing Fault and Bengal Basin. Through regional stress analysis, considering areas from central Tibet, around the eastern Himalaya Syntaxis, to Burma, it has been determined that the principal compressive stress directions align with the principal strain rates. The northeast-southwest oriented compressive stress direction from the western Shan Plateau continues into Burma. Notably, P axes align with the topographic gradients, and T axes are sub-parallel to the topographic contours in the Shan Plateau region south of 27 degrees N. These stress patterns are consistent with a gravitational potential energy induced crustal and mantle flow. The alignment of the fast shear wave with the maximum strain rate and the colinear NW-SE to E-W fast direction of the SKS wave and T axis determined from focal mechanisms in the Shan Plateau suggest that the mantle lithosphere deforms in concert with the crust. We suggest crust and mantle flow south of the Red River Fault has resulted in widening of the lithosphere in the Shan Plateau in an east-west direction. Therefore, the Sagaing Fault has bowed approximately 50-100 km westward if we assume that the Sagaing Fault was originally straight. Our results of regional stress inversion are consistent with late Miocene to present E-W shortening in the Indo-Burma subduction zone resulting from the release of gravitational potential energy from the central Tibetan Plateau. The movements of the Earth's crust in the Indo-Burma region are partially caused by India sliding underneath southeast Asia at an angle. The Sagaing Fault, along with other strike-slip faults in the Indo-Burma area, accommodates the motion of India and Asia. Even though India and Asia pushing together mostly causes east-west compression in Burma and the far east of Bangladesh, only about half of the displacement comes from their collision. It's unclear what causes the remaining east-west displacement. We suggest that the additional compression in Bangladesh and Burma happens because of the collapse of the Tibet Plateau and the flow of the Earth's lithosphere out of central Tibet. The E-W shortening of the Burma Plate is an effect of the release of gravitational potential energy from the central Tibetan Plateau Geometry and kinematics of the sinistral faulting in the Shan Plateau are consequences of radially directed compression from fan-shaped lithospheric flow Lithospheric flow around the southeast margin of the Tibetan Plateau has affected stress in northern southeast Asia and Burma

Seismic bulletin data collected by the Iranian Seismological Center are used to image crust and mantle seismic attenuation, group velocity, and phase velocities for Lg, Pg, Sn, and Pn phases. This is possible because the peak amplitude time is picked, and amplitude measurements can be associated with the phase based on travel time plots. The group velocity is the apparent velocity of the maximum amplitude arrival and represents the combined effect of phase velocity and seismic scattering. Thus, it can be used in combination with the attenuation to identify where scattering attenuation is dominant. The Arabian–Iranian plate boundary separates low-velocity Zagros sediments from central Iran; however, in the mantle, it separates a high-velocity Arabian shield from central Iran. Scattering attenuation is low within the Arabian mantle and crust, and the Zagros sediments do not cause Lg or Pg attenuation. The Eocene Urumieh Dokhtar Magmatic Arc has high attenuation within both the crust and mantle, and while there is no partial melting in the crust, there may be some in the mantle. The northern Eocene Sistan Suture Zone shows particularly high attenuation that is accompanied by high scattering. It represents an incompletely closed ocean basin that has undergone intense alteration. The Alborz Mountains have high attenuation with some scattering.

Seismic attenuation across the US is estimated using station ML magnitude data from the USArray. Station magnitudes are recalibrated back to amplitude and back projected in a 2-D tomography. Data represent the amplitudes of the horizontal components of the Lg phase. The western US shows regions of very high attenuation and contrasts with the lesser attenuation of the eastern US. Individual attenuation anomalies can be clearly tied to regional geology. Station gains show broad regional variations that match geographic regions. Most of the high-attenuation areas are regions of high geothermal activity suggesting that intrinsic attenuation dominates over scattering attenuation. An exception is the central San Andreas Fault zone because it lacks any localized heat-flow anomaly. The US east of the Rocky Mountains is bland and contains none of the high-attenuation regions of the western US. Instead, the central US has low-attenuation patches that do not obviously correspond to geologic province. Sediments of the Gulf Coast Plain, Willison Basin and Michigan Basin do show up as intermediate attenuation while the Illinois Basin, Appalachian Basin and other basins are not apparent. In Alaska, attenuation is generally less than the western US, but still much greater than the eastern US. In southeast Alaska, the Wrangell Volcanic Field causes a sizeable high-attenuation zone. The volcanic Aleutian Mountains also have high attenuation. However, moderate to high attenuation also correlates with the tertiary sedimentary basins in Alaska. The North Slope Basin does not seem to attenuate. Thicker crust and mountain roots tend to show less attenuation, if anything, but this correspondence is most likely due to differences in temperature and seismic velocity. Heat, scattering and young sedimentary basins create seismic attenuation in the continental crust.

Using P-n-wave traveltimes from three regional distance ranges we generated P-n tomography models to investigate the 3-D nature of the uppermost mantle lid P-wave velocity structure beneath the Tibetan Plateau and surrounding regions. Significant velocity variations spatially and with depth are observed. High-velocity regions are found beneath the Himalayas and most parts of southern Tibet. These high-velocity regions can be interpreted as subducting Indian continental mantle lithosphere, accreted terranes and a cold, non-convective mantle wedge beneath central Plateau. They are disjointed suggesting that the subducting Indian lithosphere is fragmented laterally. In the western Tibetan Plateau, the high-velocity region extends northwards to the middle of Qiangtang Terrane. In the central Plateau, the high-velocity region reaches near the Bangong-Nujiang suture. The northern extent of the subducted Indian continent cannot be determined uniquely from P-n models because the Indian plate dips moderately beneath southeastern Tibet. Around the Plateau, Tarim, Qaidam, Gonghe and Sichuan basins are floored by high-velocity Asian continental blocks that keep the elevation of these basins lower than surrounding regions. We found no evidence of an ongoing southward subduction of Asian lithosphere beneath central to northeastern Tibetan Plateau. Two major P-n low-velocity anomalies are found beneath northern and northeastern Tibet, primarily within the Qiangtang and Songpan-Ganzi Terranes. The northern Tibet low-velocity mantle is situated in a continental backarc of the India-Asia continental subduction zone, and hence we interpreted this region as thin thermal lithosphere with upwelling mantle driving by the subducting Indian lithosphere. The Qilianshan is also underlain by a low-velocity mantle structure and could be related to the same upwelling in this continental backarc. A narrow N-S trending low-velocity anomaly is found beneath the Yadong-Gulu Rift and confirmed that the Lhasa Terrane is not limited to the crust, but involves the entire lithosphere. Another pronounced low P-n velocity region is observed in the southeastern Tibetan Plateau, southern Yunnan and northeastern Myanmar. This feature is probably related to backarc convection associated with the subduction and rollback of Indian oceanic slab beneath Myanmar and Yunnan province, China. International Seismological Centre, On-line Bulletin, http://www.isc.ac.uk, Internatl. Seismol. Cent., Thatcham, United Kingdom, 2016.

Lg attenuation and site responses in Northeast (NE) China are estimated by implementing the Reverse Two Station Method (RTSM) at narrow band central frequencies of 0.5, 1.0, 2.0 and 3.0 Hz using 453 earthquakes recorded by 201 seismic stations deployed in the region from 1995 to 2013. The RTSM has the advantage of removing source and site effects without requiring a priori models. Tomographic images produced at a resolution of 2 degrees x 2 degrees at all frequencies exhibit a high degree of lateral variation of Lg attenuation in NE China. The Great Xing'an, Lesser Xing'an and Songen-Zhangguangcai Ranges show Q values above 400 at all frequencies. At central frequencies of 0.5 and 1 Hz, Sanjiang Basin Songliao Basin, Erlian Basin and Hailar Basin consistently show Q values lower than 400. Holocene and Pleistocene volcanoes, including the Wudalianchi and Jingpuhi volcanic fields, also appear as regions of low Q (<400) at 0.5 and 1 Hz and at higher frequencies the effects of volcanoes diminish. At high frequencies (>= 2 Hz), the sedimentary basins show Q values higher than 400 and overall Q values increase with frequency in NE China, thus obeying a power-law frequency dependence. A linear regression of frequencies in the range of 0.25-4.5 Hz results in the parameters describing the power-law frequency dependence of the region, with an average Q(0) value of 428 and a frequency-dependent factor (eta), describing the strength of dependence, of 0.68. Overall, Lg attenuation in NE China appears to be due to thick late Cretaceous sediments, Holocene and Pleistocene volcanism, moderate to high heat flow, partial melts and variation in the thickness of the crustal wave guide. The site responses calculated at 0.5, 1.0, 2.0 and 3 Hz show a high degree of lateral variation as well as variation with frequency in NE China At 0.5 and 1.0 Hz, the Great Xing'an and Lesser Xing'an Ranges show deamplification while the Hailar, Erlian and southern Songliao basins and the Songen-Zhangguangcai Range show amplification. At higher frequencies (>= 2 Hz), the pattern nearly reverses, with deamplification east of the Songliao Basin and amplification to the west of the Basin. The deamplification observed east of the Songliao Basin could be caused by basaltic lava flows resulting from Cenozoic volcanism in the region.

Using — Seismic amplitude data can be directly measured to look at regional attenuation. I used amplitude data from the dense China network that were originally collected for magnitude measurements. These measured amplitudes are generally from the Lg and Sg seismic phases and are dominated by shear-waves. Frequency dependent exponential models are used. The tomography problem inverts for regional geometric spreading, station gains, source corrections as well as the varying attenuation. Using the log-amplitude of the amplitudes linearizes the problem, cor-rects the non-Gaussian noise back to Gaussian, and gives images of higher quality than that obtained from travel time data. Results show grabens and basins have high attenuation with Q values near 100. Crystalline surface rocks typically show low attenuation with Q values near 1000. Low Q values along the edge of the Tibetan Plateau may be due to phase blockage occurring as a result of the rapid change in crustal thickness.

Nishath R. Ranasinghe,1 Andrea C. Gallegos,1 Andrea R. Trujillo,1,2 Alexander R. Blanchette,1 Eric A. Sandvol,3 James Ni,1 Thomas M. Hearn,1 Youcai Tang,4,5 Stephen P. Grand,4 Fenglin Niu,5,6 Yongshun J. Chen,7 Jieyuan Ning,7 Hitoshi Kawakatsu,8 Satoru Tanaka9 and Masayuki Obayashi9 1Department of Physics, New Mexico State University, Las Cruces, NM 88001, USA. E-mail: nrana001@nmsu.edu 2Apache Corporation, 303, Veterans Airpark Lane, #600, Midland, TX 79705, USA 3Department of Geological Sciences, University of Missouri, 101 Geology Bldg., Columbia, MO 65211, USA 4Jackson School of Geosciences, The University of Texas at Austin, Austin, TX 78712, USA 5State Key Laboratory of Petroleum Resource and Prospecting and Unconventional Natural Gas Institute, China University of Petroleum, Beijing 102249, China 6Department of Earth Science, MS-126, Rice University, Houston, TX 77005, USA 7Institute of Theoretical and Applied Geophysics, SESS, Peking University, Beijing, China 8Earthquake Research Institute, The University of Tokyo, Tokyo, Japan 9Institute for Frontier Research on Earth and Evolution, Japan Agency for Marine–Earth Science and Technology, Yokosuka, Japan

Data from recent INDEPTH IV and other broadband deployments in Tibet are used to invert for crustal delays and Pn velocities beneath the eastern Tibetan Plateau and surrounding regions.The average Pn velocity for the region is 8.1 km/s but varies from 7.8 to over 8.3 km/s.Generally low Pn velocities are found in the northeastern Tibet in the Qiangtang and Songpan-Garze terrains.This includes a zone of very low Pn velocity northwest of the Longmen Shan thrust,along the eastern Kunlun fault,and beneath the eastern Qilian Shan.A region of high Pn velocity underlies the eastern end of the Bangong-Nujiang Suture(bounded by 31—33°N;90—98°E).It could represent part of the underthrusting Indian shield.The region between the Qilian Shan and Kunlun Shan is also characterized by high Pn velocity with several zones of extremely high velocity.This includes two high velocity features beneath Qaidam basin and Gonghe basin.These features may correspond to cratonic fragments that accreted during the closure of the Tethys Ocean and have impeded,but not stopped,the northward growth of the plateau.The station delays show the thickest crust is beneath Tanggula Shan in central Tibet and should be the result of the internal deformation within Qiangtang terrain due to the collision of Indian and Eurasia plates.There is a significant decrease of crustal thickness in the northeast plateau and lateral variation also exists within the region.

The Q of seismic phase Lg is measured to approach the crustal Qβ, which can be used to infer crustal rheology. A reverse two‐station/event method is used to measure the interstationQLg, which theoretically eliminates effects from the source and site response. Strong azimuthal anisotropy of 1/QLg in northern Tibet is observed, which approximately correlates with the seismic velocity anisotropy observed using both surface waves and teleseismic S waves. Both the intrinsic and scattering attenuation contribute the isotropic Q, whereas the anisotropic Q may be associated with the fractures and faults in the crust. Strong 1/QLgis observed in the northwestern Songpan‐Ganzi fold belt, where the high‐Qdirections correspond with the orientations of major strike‐slip faults. Intrinsic and scatteringQ values are estimated for different tectonic terranes in eastern Tibetan Plateau. The intrinsic Qvalues are approximately 500 in the northern Tibetan Plateau, which suggests a hot (∼700°C) crust, consistent with low seismic velocity measurements. Our result suggests that the crust of northwestern Songpan‐Ganzi fold belt may be hotter than that of the Qiangtang terrane, which may be related to the strain heating along the major strike slip fault zones that dominate the northernmost Tibet.

Shear wave splitting measurements using teleseismic SKS and SKKS phases recorded by the INDEPTH‐IV arrays has revealed a strong upper mantle anisotropic fabric in northeastern Tibet with large delay times of up to 2.2 s, suggesting that anisotropy exists in both the lithospheric and asthenospheric mantle. The coherence among fast polarization orientations of split core phases and the left‐lateral slip on eastern‐striking, southern‐striking faults in eastern Tibet and the surface deformation fields calculated from both GPS observations and Quaternary fault slip rates support the idea that left‐lateral shear strain is the predominant cause of the orientation of the upper mantle petrofabrics. We suggest the bending of the Eastern Himalayan Syntaxis around the foundering Burma‐Andaman‐Sumatra slab also contributes to the observed seismic anisotropy in the Eastern Himalayan Syntaxis region. Two plausible competing processes are proposed for the flow of asthenosphere in eastern Tibet. In the first, the deforming lithosphere glides over the passive asthenosphere inducing flow in the asthenospheric mantle. In the second, the asthenosphere beneath northeastern Tibet is squeezed between the advancing Indian continental lithosphere and the thick Tarim and Qaidam lithospheric blocks to the north. A westward retreat of the Burma slab from Eurasia may induce flow that is toroidal and located exclusively around the northern edge of the slab. The rotation of fast orientations for stations in the Eastern Himalayan Syntaxis region are consistent with the toroidal flow pattern as well as the rotational deformation of the overlying lithosphere.

Due to the non-uniform seismic station coverage in Tibet, critically important questions remain about the existence of southward continental subduction of Eurasia beneath northern Tibet from north, and the nature of the underthrusting Indian lithosphere underneath southern Tibet from south. Using differential P- and S-wave travel-times measured from 301 stations of all the temporary experiments deployed throughout Tibet, we constructed a comprehensive tomographic model. The upper mantle of northern Tibet consists of a rather homogeneous low velocity zone with no evidence of southward Asian continental subduction. In contrast the upper mantle from the Himalayas to central Tibet exhibits laterally variable P- and S-wave velocities. Significant low velocity zones are observed that are elongated in a north–south direction and extending to at least 150km depth, which we interpret as evidences for fragmentation of the underthrusting Indian continental lithosphere.

We use receiver functions calculated for data collected by the INDEPTH‐IV seismic array to image the three‐dimensional geometry of the crustal and upper mantle velocity discontinuities beneath northeastern Tibet. Our results indicate an average crustal thickness of 65 to 70 km in northern Tibet. In addition, we observe a 20 km Moho offset beneath the northern margin of the Kunlun Mountains, a 10 km Moho offset across the Jinsha River Suture and gently northward dipping Moho beneath the Qaidam Basin. A region in the central Qiangtang Terrane with higher than normal crustal Vp/Vs ratio of ∼1.83 can be the result of the Eocene magmatic event. In the Qiangtang Terrane, we observe a significant lithospheric mantle discontinuity beneath the Bangong‐Nujiang Suture at 80 km depth which dips ∼10° to the north, reaching ∼120 km depth. We interpret this feature as either a piece of Lhasa Terrane or remnant oceanic slab underthrust below northern Tibet. We detect a ∼20 km depression of the 660‐km discontinuity in the mantle transition zone beneath the northern Lhasa Terrane in central Tibet, which suggests this phase transition has been influenced by a dense and/or cold oceanic slab. A modest ∼10 km depression of the 410‐km discontinuity located beneath the northern Qiangtang Terrane may be the result of localized warm upwelling associated with small‐scale convection induced by the penetration of the sinking Indian continental lithosphere into the transition zone beneath the central Tibetan Plateau.

The Q of regional seismic phases Lg and Pg within the crust is assumed as a proxy for crustal Q(beta) and Q(alpha), which is used as a constraint of crustal rheology. We measure regional-phase Q of the eastern Tibetan Plateau and adjacent areas. This method eliminates contributions from source and site responses and is an improvement on the Two-Station Method (TSM). We have generated tomographic images of crustal attenuation anomalies with resolution as high as 1 degrees. In general we observe low Q in the northernmost portions of the Tibetan Plateau and high Q in the more tectonically stable regions such as the interior of the Qaidam basin. The calculated site responses appear to correlate with topography or sediment thickness. Furthermore the relationship between earthquake magnitudes and calculated source terms suggest that the RTM method effectively removes the source response and may be used as an alternative to source magnitude. Citation: Bao, X., E. Sandvol, J. Ni, T. Hearn, Y. J. Chen, and Y. Shen (2011), High resolution regional seismic attenuation tomography in eastern Tibetan Plateau and adjacent regions, Geophys. Res. Lett., 38, L16304, doi:10.1029/2011GL048012.