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Temporal Change of Shallow Material During Kumamoto Earthquake by Autocorrelation Function and Interfrometry Method

Session: How Well Can We Assess Site Effects So Far? III

Type: Oral

Date: 4/21/2021

Presentation Time: 02:00 PM Pacific

Description: 

We analyze the variations of subsurface seismic properties associated to the successive shaking of the 2016 Mw 7.3 Kumamoto foreshocks, mainshock and aftershocks. We use autocorrelation functions and interferometery methods as suggested recently by Bonilla et al. (2019). The used data was recorded by surface and borehole sensors at the KiK-net stations over a period of 8 years. The seismic velocity of subsurface exhibits clear changes during the earthquake followed by a recovery phase. We observe a decrease of about 30% of seismic velocity during the mainshock, showing average changes of shallow material properties between borehole and surface stations by using the interferometry method. Using autocorrelation technique, we detect about 60% decrease of seismic velocity during the mainshock ground motion, showing the velocity changes of material properties just below the surface sensor. In a further analysis, we analyze the memory properties of material by using the velocity changes during the peak ground acceleration. It shows a gradual decrease in velocity changes after the mainshock. In addition, we analyze the variation of shear modules based on shear strain and also Vs30, which show degradation of shear modulus in the mainshock and healing process of shear modulus. Such observation can be used to improve estimate of seismic shaking hazard, site effect, and healing process of material.

Presenting Author: Reza Dokht Dolatabadi Esfahani

Student Presenter: Yes

Authors