Japan Geoscience Union Meeting 2022

Presentation information

[J] Oral

S (Solid Earth Sciences ) » S-SS Seismology

[S-SS08] Crustal Structure

Wed. May 25, 2022 1:45 PM - 3:15 PM 103 (International Conference Hall, Makuhari Messe)

convener:Mikiya Yamashita(National Institute of Advanced Industrial Science and Technology), convener:Ryosuke Azuma(Recearch Center for Prediction of Earthquake and Volcanic Eruption, Graduate School of Science, Tohoku University), Chairperson:Kazunori Yoshizawa(Faculty of Science, Hokkaido University)

2:45 PM - 3:00 PM

[SSS08-05] 2015 Gorkha Earthquake Rupture Zone Imaged from Local Earthquake Tomography

*Chintan Timsina1, James Mori2, Masumi Yamada2, Shiro Ohmi2 (1.Graduate School of Science, Kyoto University, 2.Disaster Prevention Research Institute, Kyoto University)


The 2015 MW 7.8 Gorkha earthquake caused severe damage in central Nepal. The earthquake initiated ~80 km west of Kathmandu and propagated unidirectionally toward the east along the down-dip portion of Main Himalayan Thrust (MHT). Several major aftershocks followed this event, including an MW 7.3 near the eastern edge of the mainshock rupture. Lateral variation of physical properties along the fault zone may influence the co- and post-seismic behavior of large earthquake. To identify the physical heterogeneities and its relation to the rupture characteristics of the Gorkha earthquake, we perform velocity and attenuation tomography in central Nepal.

We used an aftershock dataset that was recorded by the temporary aftershock monitoring network. For the velocity tomography, we utilized ~42,000 P- and ~29,000 S- arrivals from 1854 events with an azimuthal gap <240° and at least 10 P- and 6 S-phase observations. To ensure the smooth model even in areas with sparse ray coverage, we applied a staggered inversion workflow starting with an estimation of a 1D velocity model, followed by a 2D model, a coarse 3D model, and finally, a fine 3D model. For the attenuation tomography, first we modeled the P- and S-wave amplitude spectra for the path-averaged, frequency-independent attenuation operator (t*) using a non-linear least square technique by assuming a ω-2 source model for the frequency band of 1-30 Hz. We obtained ~17,000 t* observations for P and ~19,000 t* observations for S, which are then inverted for attenuation structure in terms of quality factor (Qp and Qs) models.

We interpret our velocity and attenuation models in terms of mineralogical compositions, petrological properties, and fluid content of the region. We select multiple published geometries of the MHT in central Nepal. We project those geometries through our 3D models to identify the lateral variations of heterogeneities on the fault zones. We further correlate these heterogeneities to the preseismic coupling, rupture of the Gorkha earthquake and postseismic deformation following the Gorkha earthquake sequence in the central Nepal.