Velocity Changes Associated to the 2019 Ambon Earthquake Using Ambient Seismic Noise
Ahmad Amiruddin (a*), Nanang T. Puspito (b), David P. Sahara (b), Andri D. Nugraha (c), Zulfakriza (d)

a) Earth Science Study Program, Faculty of Earth Science and Technology, Bandung Institute of Technology (ITB)
*ahmadamir2626[at]gmail.com
b) Global Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Bandung Institute of Technology (ITB)

Abstract

Seismic velocity changes which occurred before, during and after large magitude earthquake carry information about damage fault surrounding the area. Research focused in Ambon 6.6 Mw earthquake on September 26, 2019. We use ambient noise cross-correlation technique to compute empirical Green^s Function between station pairs from January to December 2019. We use doublet method to determine pertubation calculated in frequency domain by using Moving Windows Cross Spectrum in frequency between 0.1 to 1.0 Hz. Our results show no obvious significant velocity change before the mainshock. Velocity fluctuation average about 0.1% caused by nonisotropic of noise source around the area. Sudden velocity decrease occurred and reach average value of 0.33% in seven days after mainshock. After reach its lowest value, velocity gradually increased about 0.4% in 14 days. Velocity fluctuations about 0.2% also occurred for three months after the earthquake which may caused by the aftershocks around the earthquake epicenter. Following the large magnitude mainshock, velocity reduction may be induced by poroelastic opening and fractures due to deformation. While the velocity increase may caused by post-seismic relaxation due to elastic behavior and crack healing of the fault throughout the surrounding region.

Keywords: velocity variation, ambient noise, earthquake, seismic

Topic: Solid Earth Sciences