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- Title
The 2015 Gorkha Earthquake: Earthquake Reflection Imaging of the Source Fault and Connecting Seismic Structure With Fault Slip Behavior.
- Authors
Kurashimo, Eiji; Sato, Hiroshi; Sakai, Shin'ichi; Hirata, Naoshi; Gajurel, Ananta Prasad; Adhikari, Danda Pani; Subedi, Krishna Prasad; Yagi, Hiroshi; Upreti, Bishal Nath
- Abstract
A seismic array observation across the central focal area of the 2015 Gorkha earthquake was conducted to investigate aftershock distribution and crustal structure. Most aftershocks near Kathmandu were located above the Main Himalayan Thrust (MHT). Earthquake reflection imaging revealed the geometry of the MHT, which lies at ~10‐km depth at 75 km away from the Main Frontal Thrust. We found three areas of seismic velocity variability around the MHT above 15 km depth: (1) a high‐Vp zone where the MHT changes its dip angle from 5° to 13°, coinciding with a local maximum in coseismic slip, (2) a low‐Vp zone showing less coseismic slip, and (3) a high‐Vp zone where coseismic slip decreased further but afterslip occurred. These differences in slip behavior may indicate changes in frictional properties on the fault, which are reflected in the heterogeneity of the velocity structure. Plain Language Summary: On 25 April 2015, the Gorkha earthquake (Mw 7.8) struck central Nepal and resulted in nearly 9,000 fatalities. Destructive earthquakes have occurred repeatedly in the Himalayan region. The Himalayan seismogenic zone is located in the India‐Eurasia plate collision zone where the Indian plate underthrusts the Eurasian plate along the Main Himalayan Thrust. Revealing the crustal structure of the India‐Eurasia plate collision zone is important to constraining the process of earthquake occurrence and the orogenic process. Seismic array observation is an effective tool to investigate the crustal structure. Here, we present the results of seismic array observation across the central focal area of the 2015 Gorkha earthquake, which shows the geometry of the Main Himalayan Thrust and seismic velocity variability along its length. We find a high‐Vp zone which coincides with a large coseismic slip zone (>6 m). A low‐Vp zone shows less coseismic slip. Another high‐Vp zone located in the southern side of the low‐Vp zone corresponds to an area of afterslip. These results connect heterogeneous crustal structure with fault slip behavior and suggest that variability in the seismic properties of the crustal structure around the plate boundary may affect fault slip behavior. Key Points: Source fault geometry of the 2015 Gorkha earthquake can be imaged by using an earthquake reflection imaging methodA high‐Vp zone where the dip angle of the Main Himalayan Thrust changes coincides with the area of maximum coseismic slipHeterogeneous crustal structure around the Main Himalayan Thrust reflects changes in the frictional properties of the fault
- Subjects
NEPAL Earthquake, 2015; EARTHQUAKE hazard analysis; PLATE tectonics; EARTHQUAKE magnitude; EARTHQUAKE resistant design; SEISMOLOGY
- Publication
Geophysical Research Letters, 2019, Vol 46, Issue 6, p3206
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2018GL081197