Analysis of subsurface Resistivity Structures in Relation to the Level of Damage Caused by Earthquakes Using the Audio-Magnetotelluric (AMT) Method (Case study: The 2006 Yogyakarta Earthquake)

Abstract

The 2006 Yogyakarta Earthquake had caused a disaster in Bantul area. Although the magnitude reached only Mw = 6.4, it left more than 6,000 fatalities and up to 1,000,000 homeless. The earthquakes that occur in this area is shallow earthquakes that originate on land (Opak fault) and triggers quite high surface damage. This damage includes damage to buildings and infrastructure that support community activities. The main objective of this research is to determine the subsurface structure and be able to identify soft layers based on the distribution of resistivity values that can be correlated to the value of the amplification factor. The Audio-Magnetotelluric (AMT) method was conducted in this area using five components of electric and magnetic fields. The Audio-Magnetotelluric (AMT) method utilizes electromagnetic waves with a frequency of 1 Hz to 100KHz. Based on the one-dimensional (1-D) inversion result calculated from 3 sites show that there is a low resistivity value (10 - 70 ωm) from the surface to the depth of 1000 m. This ticked conductive zone interpreted as a sediment layer that can triggers the high amplification factor values.