ANALISIS INDEKS BAHAYA GEMPA BUMI BERDASARKAN PGA PERMUKAAN DI KECAMATAN SANDEN KABUPATEN BANTUL D.I. YOGYAKARTA

Abstract

This research is motivated by the earthquake phenomena that have occurred in the Yogyakarta area due to the
2006 earthquake. This study aims to determine the earthquake hazard index based on the method developed by
BNPB and JICA by making earthquake hazard distribution maps correlated with settlement maps. This research
was conducted in Sanden District in the south of Bantul Regency. The BNPB and JICA methods utilize four main
parameters, namely shear wave velocity at a depth of 30 meters (Vs30), Ground Amplification Factor (GAF),
accelerated ground rock vibration (PGASB) and acceleration of surface ground vibration (PGA). Vs30 is obtained
from the inversion method using microtremor measurement data, the Vs30 value is converted into a GAF value
using the formula Midorikawa et al (1994), for PGASB it is obtained from the PUSKIM website, based on the
earthquake hazard index mapping guide the Vs30 and PGASB values obtained if multiplied then will get the surface
PGA value then the surface PGA value is reclassified by the type of class based on the BNPB and JICA methods.
The results showed that the value of Vs30 ranged from 154.66 m / s to 260.80 m / s, GAF values ranged from 1.64
g to 2.09 g, PGASB values ranged from 0.52 g to 0.67 g, and PGA values surface ranges from 0.87 to 1.32 g. The
earthquake hazard index covers the entire Sanden District with an index value of 1 and the highest distribution of
settlements prone to earthquake hazards is in the entire study area.
Keywords: Microtremor, Vs30, GAF, surface ground vibration acceleration (PGA), PGASB, earthquake.