STUDI MIKROSEISMIK UNTUK MENDETEKSI PERUBAHAN GARIS PANTAI DENGAN INDIKATOR INDEKS KERENTANAN SEISMIK, PEAK GROUND ACCELERATION DAN GROUND SHEAR STRAIN DI PROVINSI BENGKULU

Shores of Bengkulu Province are geographically located in the subduction zone between the Indian-Australian plate and the Eurasian plate, so it is often hit by earthquakes. Many researchs have been done to correlate the power of the earthquake with the impact of damages. This research aims to: (1) determine the characteristics of the seismic vulnerability index based on microseismic data, peak ground acceleration and ground shear strain on any types of beach in Bengkulu province and correction with the rate of change shorelines. For the purposes of this research, it has been carried out taking 127 points of microseismic data along the shore of Bengkulu by using short-period seismometers with 3 components. The measurements for each point was 30 minutes. Data collection was not done by gridding, but by specifying the type of beach. Data collection points aretaken for each type of shore. The amount of data taken at each type of beach based onthe areaof type shore. For the type of flat fine sandy beach, it was taken 21 points, a flat rocky beach was taken 12 points, 12 points of beach muddy flat, flat sandy beaches rugged was taken 20 points, steep rocky lava beach was taken 15 points, steep rocky coast clay was taken 20 points, steep rocky coast tuffaceous clay was 16 points, and tufa steep sandy beach stone was taken 15 points. Historical data of earthquakes in 1900 to 2009 are other supporting data. The data were processed using Geopsy to obtain the spectrum. The validation of microseismic spectrum to obtain a reliable spectrum refers to the rules of SESAME 2004, obtained 122 reliable spectrums and unreliable spectrums. The validation is done for obtaining clear peak, obtained 97 spectra that show clear peaks and 30 did not show the clear spectral peaks. The microseismic data were analyzed quantitatively through Horizontal to Vertical Spectral Ratio (HVSR), while the earthquake history of the data were processed by using the attenuation equation. There are two attenuation equations, (1) Kanai and (2) Fukushima-Tanaka equation. The results showed that the average value of the seismic vulnerability index based on microseismic changed with the type of shore . The average value for the seismic vulnerability index (1) the type of flat fine sandy beach is 2.1 , (2) a muddy flat beach is 7.6 , (3) a flat rocky beach is 0.5 , (4 ) coarse sandy flat beach is 2.9 , (5) a steep rocky lava beach is 1.3 , (6) the steep rocky shore clays is 16.