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DOE OSTI2015

Relocation of the 2010-2013 near the north coast of Papua earthquake sequence using Modified Joint Hypocenter Determination (MJHD) method

The accuracy of earthquake hypocenter position is necessary to analyze the tectonic conditions. This study aims to: (1) relocate the mainshock and aftershocks of the large earthquakes in Papua region i.e. June 16, 2010, April 21, 2012 and April 06, 2013 earthquake (2) determine the true fault plane, (3) estimate the area of the fracture, and (4) analyze the advantages and disadvantages of relocation with MJHD method in benefits for tectonic studies. This study used Modified Joint Hypocenter Determination (MJHD) method. Using P arrival phase data reported by the BMKG and openly available from website repogempa.bmkg.go.id, we relocated the mainshock of this large significant earthquake and its aftershocks. Then we identified the prefered fault planes from the candidate fault planes provided by the global CMT catalogue. The position of earthquakes was successfully relocated. The earthquakes mostly were clustered around the mainshock. Earthquakes that not clustered around mainshock are considered to be different mechanism from the mainshock. Relocation results indicate that the mainshock fault plane of June 16, 2010 earthquake is a field with strike 332o, dip 80o and −172o slip, the mainshock fault plane of April 21, 2012 earthquake is a field with strike 82o, dip 84o and 2o slip, the mainshock fault plane of April 06, 2013 earthquake is a field with strike 339o, dip 56o and −137o slip. Fault plane area estimated by cross section graphical method is an area of 2816.0 km2 (June 16, 2010), 906.2 km2 (April 21, 2012) and 1984.3 km2 (April 06, 2013). MJHD method has the advantage that it can calculate a lot of earthquakes simultaneously and has a station correction to account for lateral heterogeneity of the earth. This method successfully provides significant changes to improve the position of the depth of earthquakes that most of the hypocenter depth manually specified as a fixed depth (± 10 km). But this method cannot be sure that the hypocenters derived from the same earthquake mechanism.

58 GEOSCIENCES↗

DOE OSTI2015

Analyzing the subsurface structure using seismic refraction method: Case study STMKG campus

A geophysic survey is performed to detect subsurface structure under STMKG Campus in Pondok Betung, South Tangerang, Indonesia, using seismic refraction method. The survey used PASI 16S24-U24. The waveform data is acquired from 3 different tracks on the research location with a close range from each track. On each track we expanded 24 geofons with spacing between receiver 2 meters and the total length of each track about 48 meters. The waveform data analysed using 2 different ways. First, used a seismic refractionapplication WINSISIM 12 and second, used a Hagiwara Method. From both analysis, we known the velocity of P-wave in the first and second layer and the thickness of the first layer. From the velocity and the thickness informations we made 2-D vertical subsurface profiles. In this research, we only detect 2 layers in each tracks. The P-wave velocity of first layer is about 200-500 m/s with the thickness of this layer about 3-6 m/s. The P-wave velocity of second layer is about 400-900 m/s. From the P-wave velocity data we interpreted that both layer consisted by similar materials such as top soil, soil, sand, unsaturated gravel, alluvium and clay. But, the P-wave velocity difference between those 2 layers assumed happening because the first layer is soil embankment layer, having younger age than the layer below.

58 GEOSCIENCES↗