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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Using Pn -wave traveltimes from three regional distance ranges we generated Pn 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 Pn 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 Pn 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 Pn 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. [ABSTRACT FROM AUTHOR]

The 127 station NorthEast China Extended SeiSmic Array (NECESSArray) provides large quantities of high quality seismic data in northeast China that allow us to resolve lateral variations of Lg Q or crustal attenuation at 1 Hz (Qo)to2.0° or greater. Using the reverse two-station/event method with 11 642 Lg path-amplitudes from 78 crustal earthquakes, we obtain a 2-D tomographic image of Lg Qo with values ranging from -50 to 1400. A high degree of detail in the lateral variation of Lg attenuation is revealed in our tomographic image. High Qo regions are found in the Great Xing'an, Lesser Xing'an and Songen-Zhangguangcai Ranges. Low Qo regions are observed in the Songliao, Sanjiang and Erlian Basins. The lowest Qo is found near the Wudalianchi volcanic field and other Quaternary volcanic fields, the southern Songliao Basin, the western edge of the Erlian Basin and the Sanjiang Basin. Low Qo values are measured for paths that cross sedimentary basins with thick, unconsolidated sediments. Most of the high Lg attenuation in the Songliao Basin correlates reasonably well with low crustal Rayleigh wave phase velocity anomalies. The highest attenuating regions also correlate well with regions of Holocene volcanism. [ABSTRACT FROM AUTHOR]

Amplitude tomography reconstructs seismic attenuation directly from recorded wave amplitudes. We have applied the tomography to amplitude data reported in the ‘Annual Bulletin of Chinese Earthquakes’ and interpreted the regionally varying crustal attenuation in terms of tectonics. The seismic amplitudes were originally recorded for determining the ML and MS magnitudes. They generally correspond to the maximum amplitudes of the horizontal components of the short-period S waves and intermediate-period Rayleigh waves. Both sets of measurements are sensitive to crustal structure. The peak amplitudes from ML amplitudes spread spherically with significant dispersion and scattering. MS amplitudes show cylindrical spreading with little dispersion. Average crustal Q values for attenuation at 1 Hz are 737 and 505 for ML and MS, respectively, with substantial regional variations. Frequency dependence in the attenuation is also indicated. Regions with the lowest attenuation (high Q values) are beneath the south China Block, Sichuan Basin, Ordos Platform, the Daxinganling and the Korea Craton. These tend to be tectonically inactive regions, which are generally dominated by intrusive and cratonic rocks in the upper crust. Regions with the highest attenuation (low Q values) are beneath Bohai Basin, Yunnan, eastern Songpan-Ganzi Terrain, margins of the Ordos platform and the Qilian Shan. These are predominantly active basins, grabens and fold belts. The continental margin also highly attenuates both S and surface waves. [ABSTRACT FROM AUTHOR]

We have selected 10,899 ML amplitude readings from 1732 events recorded by 91 stations, as reported in the Annual Bulletin of Chinese Earthquakes (ABCE), and have used tomographic imaging to estimate the lateral variations of the quality factor Q0 (Q at 1 Hz) within the crust of Northern China. Estimated Q0 values vary from 115 to 715 with an average of 415. Q0 values are consistent with tectonic and topographic structure in Eastern China. Q0 is low in the active tectonic regions having many faults, such as the Shanxi and Yinchuan Grabens, Bohai Bay, and Tanlu Fault Zone, and is high in the stable Ordos Craton, Q0 values are low in several topographically low-lying areas, such as the North China, Taikang-Hefei, Jianghan, Subei-Yellow Sea, and Songliao basins, whereas it is high in mountainous and uplift regions exhibiting surface expressions of crystalline basement rocks: the Yinshan, Yanshan, Taihang, Qinlin, Dabie and Wuyi Mountains, and Luxi and Jiaoliao Uplifts. Quality-factor estimates are also consistent with Pn- and Sn-velocity patterns. High-velocity values, in general, correspond with high Q0 and low-velocity values with low Q0. This is consistent with a common temperature influence in the crust and uppermost mantle. [ABSTRACT FROM AUTHOR]