Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis
AbstractThe optimum 1D velocity model is calculated for the Kinnaur sector of the NW Himalaya utilizing the arrival time information of the local earthquakes (137 no.) recorded with 12 broadband seismic network within the azimuthal gap of ≤180°. This optimum 1D velocity model is a fi...
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GeoScienceWorld
2022-02-01
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| Series: | Lithosphere |
| Online Access: | https://pubs.geoscienceworld.org/lithosphere/article/2021/Special%206/2834594/611069/Velocity-Structure-and-Deep-Earthquakes-beneath |
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| author | Shubhasmita Biswal Sushil Kumar Keith Priestley W. K. Mohanty Mahesh Prasad Parija |
| author_facet | Shubhasmita Biswal Sushil Kumar Keith Priestley W. K. Mohanty Mahesh Prasad Parija |
| author_sort | Shubhasmita Biswal |
| collection | DOAJ |
| description |
AbstractThe optimum 1D velocity model is calculated for the Kinnaur sector of the NW Himalaya utilizing the arrival time information of the local earthquakes (137 no.) recorded with 12 broadband seismic network within the azimuthal gap of ≤180°. This optimum 1D velocity model is a five-layer model and ranges from the surface to 90 km in the shallow mantle. P velocity varies from 5.5 km/s to 8.6 km/s in the crust and upper mantle, and S-wave velocity varies between 3.2 km/s and 4.9 km/s for the same range. When we relocated the earthquakes with the Joint Hypocenter Determination program incorporating the optimum 1D velocity model, it resulted in a lower RMS residual error of 0.23 s for the hypocenter locations compared to initial hypo71 locations. A total of 1274 P and 1272 S arrival times were utilized to compute station delays. We observed positive variations in P-station delays from -0.19 s below the PULG station to 0.11 s below the SRHN station. Similarly, for S-station delays, we observed negative delays at each individual site from -0.65 s at LOSR station to -0.16 s at the SRHN station. This large variation in P- and S-station delays corresponds to the 3D nature of the subsurface below the Kinnaur Himalaya. The relocated seismicity is clustered along the STD fault at sub-Moho and Moho depths ranging between 40 km and 80 km. The seismicity distribution aligned across the strike of the STD and along the strike of the Kaurik-Chango fault (KCF) can be attributed to the cross-fault interactions of the KCF and the STD fault in the area. We also observed bimodal depth distribution of seismicity in the Higher and Tethys Himalayas. The occurrence of earthquakes down to a depth of ~0-40 km and 50-80 km in the study area can be interpreted in terms of stress contribution from interseismic stress loading associated with the India-Eurasia collision tectonics. The presence of hypocentres in the shallow mantle at 120 km depth highlights the strength of the mantle, which seems to be deforming in a brittle manner below the region. The computed focal mechanisms exhibit generally the flexing of the Indian plate below the Lesser Himalaya with shear parallel to the strike of the MCT and extension orthogonal to it. This study shows deformation over the entire crust and shallow upper mantle levels, with differential stress conditions. Thus, we can consider the crust and the shallow upper mantle down to depths of 120 km to be seismogenic in nature and is capable of producing the microseismicity beneath the Kinnaur Himalaya. |
| first_indexed | 2024-12-12T17:16:05Z |
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| id | doaj.art-8d0481934a57458d9711d03c1935509d |
| institution | Directory Open Access Journal |
| issn | 1941-8264 1947-4253 |
| language | English |
| last_indexed | 2024-12-12T17:16:05Z |
| publishDate | 2022-02-01 |
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| series | Lithosphere |
| spelling | doaj.art-8d0481934a57458d9711d03c1935509d2022-12-22T00:17:47ZengGeoScienceWorldLithosphere1941-82641947-42532022-02-012021Special 610.2113/2022/2834594Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor AnalysisShubhasmita Biswal0http://orcid.org/0000-0003-4682-9407Sushil Kumar1http://orcid.org/0000-0001-5536-3384Keith Priestley2W. K. Mohanty3Mahesh Prasad Parija4http://orcid.org/0000-0001-7441-2882Department of Geology and Geophysics Indian Institute of Technology Kharagpur Kharagpur 721302 India iitkgp.ac.inWadia Institute of Himalayan Geology Dehradun 248001 Uttarakhand IndiaBullard Laboratories University of Cambridge Cambridge UK cam.ac.ukDepartment of Geology and Geophysics Indian Institute of Technology Kharagpur Kharagpur 721302 India iitkgp.ac.inNational Geophysical Research Institute Hyderabad 500007 Telangana India ngri.org.in AbstractThe optimum 1D velocity model is calculated for the Kinnaur sector of the NW Himalaya utilizing the arrival time information of the local earthquakes (137 no.) recorded with 12 broadband seismic network within the azimuthal gap of ≤180°. This optimum 1D velocity model is a five-layer model and ranges from the surface to 90 km in the shallow mantle. P velocity varies from 5.5 km/s to 8.6 km/s in the crust and upper mantle, and S-wave velocity varies between 3.2 km/s and 4.9 km/s for the same range. When we relocated the earthquakes with the Joint Hypocenter Determination program incorporating the optimum 1D velocity model, it resulted in a lower RMS residual error of 0.23 s for the hypocenter locations compared to initial hypo71 locations. A total of 1274 P and 1272 S arrival times were utilized to compute station delays. We observed positive variations in P-station delays from -0.19 s below the PULG station to 0.11 s below the SRHN station. Similarly, for S-station delays, we observed negative delays at each individual site from -0.65 s at LOSR station to -0.16 s at the SRHN station. This large variation in P- and S-station delays corresponds to the 3D nature of the subsurface below the Kinnaur Himalaya. The relocated seismicity is clustered along the STD fault at sub-Moho and Moho depths ranging between 40 km and 80 km. The seismicity distribution aligned across the strike of the STD and along the strike of the Kaurik-Chango fault (KCF) can be attributed to the cross-fault interactions of the KCF and the STD fault in the area. We also observed bimodal depth distribution of seismicity in the Higher and Tethys Himalayas. The occurrence of earthquakes down to a depth of ~0-40 km and 50-80 km in the study area can be interpreted in terms of stress contribution from interseismic stress loading associated with the India-Eurasia collision tectonics. The presence of hypocentres in the shallow mantle at 120 km depth highlights the strength of the mantle, which seems to be deforming in a brittle manner below the region. The computed focal mechanisms exhibit generally the flexing of the Indian plate below the Lesser Himalaya with shear parallel to the strike of the MCT and extension orthogonal to it. This study shows deformation over the entire crust and shallow upper mantle levels, with differential stress conditions. Thus, we can consider the crust and the shallow upper mantle down to depths of 120 km to be seismogenic in nature and is capable of producing the microseismicity beneath the Kinnaur Himalaya.https://pubs.geoscienceworld.org/lithosphere/article/2021/Special%206/2834594/611069/Velocity-Structure-and-Deep-Earthquakes-beneath |
| spellingShingle | Shubhasmita Biswal Sushil Kumar Keith Priestley W. K. Mohanty Mahesh Prasad Parija Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis Lithosphere |
| title | Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis |
| title_full | Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis |
| title_fullStr | Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis |
| title_full_unstemmed | Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis |
| title_short | Velocity Structure and Deep Earthquakes beneath the Kinnaur, NW Himalaya: Constraints from Relocated Seismicity and Moment Tensor Analysis |
| title_sort | velocity structure and deep earthquakes beneath the kinnaur nw himalaya constraints from relocated seismicity and moment tensor analysis |
| url | https://pubs.geoscienceworld.org/lithosphere/article/2021/Special%206/2834594/611069/Velocity-Structure-and-Deep-Earthquakes-beneath |
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