Kirbani Sri Brotopuspito

Team investigates activity at Mt. Semeru, Java, volcano

In February 1994 a large eruption continued a pattern of activity that Mt. Semeru volcano—the highest mountain in Java, Indonesia—has exhibited since 1967. Mt. Semeru lies south of the Tengger Caldera, which encloses the volcano Mt. Bromo. Together, they form one of the largest volcanic complexes in the province of East Java. Although Mt. Semeru is one of the most continuously active volcanos in Indonesia, it has been the subject of few scientific investigations. Observations of the volcanos activity are made from a distance and compiled in monthly and annual reports by the Volcanological Survey of Indonesia (VSI), but the most recent detailed map of the summit region was published in 1938 in the Atlas of the Dutch Colonies.

Soft volcanic sediments compound 2006 Java earthquake disaster

When the region south of Mount Merapi volcano in central Java, Indonesia, was struck by a magnitude 6.4 earthquake, the city of Yogyakarta and its suburbs were partly devastated. The event caused severe damage to the densely inhabited area, leaving about 6000 people dead, 50,000 injured, and between 500,000 and 1 million homeless. With over 155,000 houses totally destroyed and 200,000 damaged, more houses were affected in this earthquake area than in Aceh and Nias after the earthquake-tsunami disasters of 26 December 2004 and 28 March 2005 combined [United Nations, 2006].

Designed microtremor array based actual measurement and analysis of strong ground motion at Palu city, Indonesia

In this study, we investigated the strong ground motion characteristics under Palu City, Indonesia. The shear wave velocity structures evaluated by eight microtremors measurement are the most applicable to determine the thickness of sediments and average shear wave velocity with Vs ≤ 300 m/s. Based on subsurface underground structure models identified, earthquake ground motion was estimated in the future Palu-Koro earthquake by using statistical green’s function method. The seismic microzonation parameters were carried out by considering several significant controlling factors on ground response at January 23, 2005 earthquake.

Estimation of underground structure at Prambanan area, Yogyakarta, Indonesia

In this study, we investigated the underground structure at Prambanan area, Yogyakarta. We performed single observations of microtremor at 124 sites in Prambanan area. The results enabled us to estimate the site-dependent shaking characteristics of earthquake ground motion. We also conducted 2-site bore holes investigation to gain a representative determination of the soil condition of subsurface structures in Prambanan. From the SPT of borehole observations, the prambanan area corresponds to relatively soil condition with Vs ≤ 298 m/s, the predominant periods due to horizontal vertical ratios (HVSRs) are in the range of 0.48 to 1.19 s and the frequency are in the range of 0.95 to 1.92 Hz. By making these observations, we can obtain a relationship between the predominant periods, frequency and distribution of the first layer thickness of the sediment.

Ground Shear Strain and Rate of Erosion in the Coastal Area of North Bengkulu, Indonesia

North Bengkulu district has an area prone to earthquakes, because this area is very closed to the Sumatra subduction zone to the Eurasian tectonic plate. Coastal area in this region is experiencing with the very fast erosion. This is thought to have relation with earthquake-prone zones. This study aims to find the relationship between Ground Shear Strain (GSS) and rate of erosion in the coastal area of North Bengkulu. The data of coastal erosion rate was obtained by overlaying shoreline in 1947 and 2012. The GSS can be obtained by multiplying Seismic Vulnerability Index (SVI) and Peak Ground Acceleration (PGA) values around the shoreline. Seismic Vulnerability Index was obtained by processing microseismic data acquired using three component in short period of seismometers. The PGA was obtained from the historical earthquake and calculated by using Fukushima-Tanaka equation. The results show that the value of GSS varies between 0.0001 to 0.0055, and the SVI values is ranging from 1.2 to 16.1. In addition, we estimated that PGA value is 92 to 120 and the rate of erosion between 3.6 up to 5.8 m/yr. GSS value for each type of coastal is 0.00046 for the fine sandy beach flat, 0.0043 for flat coastal muddy, 0.0001 for flat rocky beaches, 0.0006 for sandy beaches to rugged, 0.0003 for steep rocky lava beach, 0.0014 for steep rocky coast of for clay, 0.0011 for bertufa steep sandy beach stones, and 0.0014 for the steep rocky shore tuffaceous clay. It is found that the GSS value depends on the type of coastal. In this case, flat coastal muddy show highest effect on the GSS. Both SVI and GSS can be estimated to be a quadratic relation to the erosion rate.