Seismic anisotropy imposes first-order constraints on the strain history of crust and upper mantle rocks. In this study, we analyze the mantle seismic anisotropy of the Western Canada Sedimentary Basin using a new shear wave spitting data set consisting of 1,333 teleseismic arrivals from 82 seismic stations. The resulting 332 high-quality measurements yield a regional mean apparent splitting time (i.e., the magnitude of anisotropy) of 1.10.3s and an average fast orientation (i.e., the direction of anisotropy) of 54.6 degrees 17.2 degrees, which favor a two-layer anisotropic model based on the 90 degrees back azimuthal periodicity in both parameters. The northeast trending fast orientations dominate the lower layer at lithospheric depths and are approximately parallel to the present-day absolute plate motions (APMs; i.e., <35 degrees) due to the active asthenospheric flow. On the other hand, deviations from the APMs along the Canadian Rocky Mountain foothills could reflect disrupted mantle flow surrounding a southwestward migrating cratonic lithosphere. Also revealed are two elongated upper-layer anisotropic anomalies in the lithosphere that are spatially correlated with Moho depths. Their characteristics suggest frozen-in anisotropy imprinted along two convergent boundaries: (1) the Paleoproterozoic Snowbird Tectonic Zone that separates northeast (north) from northwest (south) fast directions and (2) the foothills of the Rocky Mountains that exhibit northeast trending orientations consistent with those of the APMs, maximum crustal stress, and electromagnetic anisotropy. Compressions associated with the Cordilleran orogenesis could be responsible for the spatial changes in the shear wave anisotropy from the foothills to the cratonic interior.
WU Lei
Supported by the national key R & D Program "deep processes and resource effects of Yanshanian major geological events" project "comprehensive geophysical exploration and deep processes of key corridors", we completed two OBS wide-angle seismic profiles in the East China Sea shelf area in 2017 and 2019. Based on the obtained OBS Data, the deep crustal structure of the East China Sea shelf is obtained by using the forward and inversion methods of tomography. The velocity structure reveals that the crustal thickness decreases from 30km in Zhejiang Fujian orogenic belt to 15km in continental shelf basin, and the corresponding crustal velocity changes from 4.40-7.15km/s to 4.30-6.90km/s. Based on the previous studies, we find that there are high magnetic anomalies in Zhejiang Fujian orogenic belt. We think that the crustal structure of Zhejiang Fujian orogenic belt is quite different from that of continental shelf basin. The East China Sea may not be the extension of South China continental margin; There is a high velocity anomaly with a width of about 50km and a velocity of 7.15km/s at the junction of Zhejiang Fujian orogenic belt and continental shelf basin. We speculate that the anomaly is a Mesozoic suture zone, and the high velocity anomaly is related to the magmatic activity caused by plate tearing when the paleo Pacific plate subducted and retreated.
DING Weiwei, WEI Xiaodong
The data set is the original repeated GPS observation data along Gyirong - Nyima profile trans active deformation Himalayan orogenic belt in Tibet Plateau. The data are measured twice in 2018 and 2019, including the data of 13 stations, and the data quality is good. Through the observation data of these observation points, combined with the continuous GPS observation profile data that the project research team has deployed along Yadong Gulou in the Himalayan orogenic belt, we can reveal the horizontal and vertical distribution characteristics of the northward converging strain of the Indian continent in the key parts of the Himalayan orogenic belt, understand the current uplift state of the Himalayan orogenic belt and its correlation with horizontal movement, and combine with the active faults Based on the theory of motion dislocation, the quantitative distribution of strain between earthquakes in the main boundary fault (MBT) and the main central fault (MCT) is studied, as well as the strain accumulation characteristics, fault locking range and fault locking degree between earthquakes, which provide important constraints for evaluating the seismic risk of active faults in the study area. Combined with the 2015 Nepal earthquake rupture model, the southern margin of Tibetan Plateau is studied from the perspective of motion to dynamics Lithospheric rheological characteristics.
HE Jiankun
The Pan-Third Polar region has strong seismic activity, which is driven by the subduction and collision of the Indian plate, the Arab plate and the Eurasian plate. 18806 earthquakes with Magnitude 5 or larger have occurred in Pan-Third Polar region (north latitude 0-56 degrees and east longitude 43-139 degrees) since 1960. Among them, 4 earthquakes with Magnitude 8 or larger, 187 earthquakes with Magnitude 7.0-7.9， 1625 earthquakes with Magnitude 6.0-6.9 and 16990 earthquakes with Magnitude 5.0-5.9 have occurred. Earthquakes occurred mainly in the foothills of the India-Myanmar Mountains, the Himalaya Mountains, the Sulaiman Mountains, where the India Plate collided with the Eurasian plate, and the Zagros Mountains where the Arab plate collided with the Eurasian plate.
WANG Ji
This data set is used to analyze the global activity level of strong earthquakes (Mw 5) in the past 30 years, and to present it spatially. It can be used to obtain the distribution areas of strong earthquakes with high frequency and activity level in recent years. By comparing the distribution of strong earthquakes in 2018 with that in 1989-2018, the distribution characteristics of global strong earthquakes in 2018 are obtained. The original data of strong earthquakes are from USGS, and the local density is calculated as frequency information. The magnitudes of all earthquake cases are interpolated globally, and then the frequency and magnitude are multiplied as the activity level of strong earthquakes. The data set is in TIff format with a spatial resolution of about 80 km. The data set can provide a reference for the analysis of strong earthquake activity level on the global scale, and is helpful for the analysis of global earthquake risk and the construction of earthquake prevention and disaster reduction system.
Chen Jin, Tang Hong, WU Jianjun, ZHOU Hongmin
The data includes earthquakes at various levels across the country from 2300 BC to 2005 AD. There are a total of more than 330,000 catalogs, each of which includes earthquake time, epicenter longitude, epicenter latitude, focal depth, positioning accuracy, and magnitude. This data was first released by the National Seismological Bureau. The China Earthquake Catalog contains a Mapinfo layer (Total_0510Time) and files with the extensions .TAB, .MAP, .DAT, .ID. Their functions are as follows: TAB: the main file, including the table data structure and entity data format fields; MAP: a geographic data file containing map objects; ID: the index file of the graphic object file (MAP); DAT: Form data file.
MA Jin
This data set is collected from the supplementary information part of the paper: Pei, S.P., Niu, F.L., Ben-Zion, Y., Sun, Q., Liu, Y.B., Xue, X.T., Su,J.R., & Shao, Z.G. (2019). Seismic velocity reduction and accelerated recovery due to earthquakes on the Longmenshan fault. Nature Geoscience. 12. 387-392. doi:10.1038/s41561-019-0347-1. This paper studies the structural evolution process of The Longmenshan fault zone located at a pronounced topographic boundary between the eastern margin of the Tibetan plateau and the western Sichuan basin. With the observations on coseismic velocity reductions and the healing phases, it is found that the healing phase of Wenchuan earthquake fracture zone accelerated significantly in response to the Lushan earthquake. This data set contains 3 tables, table names and content are as follows: Data list: The data name list of the rest tables; t1: Data of the four periods (befor Wenchuan earthquake, after Wenchuan earthquake, before Lushan earthquake, after Lushan earthquake); t2: The average velocities with error in Figure 2 in the paper for Wenchuan earthquake (WCEQ) and Lushan earthquake (LSEQ) area. See attachments for data details: Supplementary information.pdf, Seismic velocity reduction and accelerated recovery due to earthquakes on the Longmenshan fault.pdf.
PEI Shunping
The 2015 Gorkha, Nepal earthquake (Mw 7.8) ruptured the Main Himalayan Thrust (MHT) and allows direct measurements of the behavior of the continental collision zone. We study the MHT using seismic waveforms recorded by local stations that completely cover the aftershock zone (Event catalog 1.docx and Event catalog 2.docx). We obtained the velocity structure beneath the study zone (Velocity.dat). The MHT exhibits clear lateral variation along geologic strike, with the Lesser Himalayan ramp having moderate dip on the MHT beneath the mainshock area and a flatter and deeper MHT beneath the eastern end of the aftershock zone. East of the aftershock zone, seismic wave speed increases at MHT depths, perhaps due to subduction of an Indian basement ridge. A similar magnitude wave speed change occurs at the western end of the aftershock zone. These gross morphological structures of the MHT controlled the rupture length of the Gorkha earthquake.
The dataset is the teleseismic waveform data from the Gyirong – Peiku Tso short-period dense seismic array profile. The data can be used to receiver function methods to probe the structure of the crust and upper mantle. The Gyirong – Peiku Tso profile crosses the north-south Gyirong Rift, and the data are derived from 134 short-period seismic stations set up by the subject group along the east-west Gyirong – Peiku Tso profile, with strict site selection and good data quality. This profile provides an important scientific basis for revealing the velocity discontinuity morphology below the Chilung Rift Valley, i.e., the interfacial extension of the Indian continent swooping northward in the crust below the Himalayan zonation, and for further understanding the lateral changes of the MHT interface and the dynamics of the east-west extension of the Tibetan Plateau.
XU Qiang
The dataset partially used in the study of paper 2018GC007986 includes S receiver functions derived from 48 permanent stations and 11 stations of a temporary HY array deployed in the northeastern Tibetan Plateau. The dataset as a zipped file contains one folder, two files including NETibet_SRF.QBN and NETibet_SRF.QHD. A spiking deconvolution in the time domain is used to calculate the P and S receiver functions, all the S receiver functions have been visually inspected to remove the bad traces that obviously different from the majority. The dataset is applied to explore the lithospheric structure and understand the mechanism of northeastern expansion and growth of NE Tibetan Plateau.
XU Qiang
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