The complex geological structures in East Java and Bali provide important opportunities for natural resource exploitation, but also harbor perils associated with natural disasters. Such a condition makes the East Java region an important area for exploration of the subsurface seismic wave velocity structure, especially in its upper crust. We employed the ambient noise tomography method to image the upper crustal structure under this study area. We used seismic data recorded at 24 seismographs of BMKG spread over East Java and Bali. In addition, we installed 28 portable seismographs in East Java from April 2013 to January 2014 for 2-8 weeks, and we installed an additional 28 seismographs simultaneously throughout East Java from August 2015 to April 2016. We constructed inter-station Rayleigh wave Green's functions through cross-correlations of the vertical component of seismic noise recordings at 1500 pairs of stations. We used the Neighborhood Algorithm to construct depth profiles of shear wave velocity (Vs). The main result obtained from this study is the thickness of sediment cover. East Java's southern mountain zone is dominated by higher Vs, the Kendeng basin in the center is dominated by very low Vs, and the Rembang zone (to the North of Kendeng zone) is associated with medium Vs. The existence of structures with oil and gas potential in the Kendeng and Rembang zones can be identified by low Vs.

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Research to find out intrusion in Pangandaran is very interesting, because this area is close to coastal objects that has been expanding and leading tourist attraction in West Java, Indonesia. This intrusion information is useful to determine aquifer locations which indicate below that the location is saturated water. If this aquifer locations are detected in large areas and wide volume, then this location will have potential liquefaction during a big earthquake. This research could be used as the first step before the next research to measure and calculate on either location by detail grid and radius with these 2 lines, so it is gotten direct and large distribution of sea-water intrusion. The purpose of this study is to identify the subsurface structures to get an overview of sea-water intrusion. The method used is geoelectrical based on the electrical resistance value of the rock type. The results of the measurement of 2 lines and data processing showed that the line in Pesona Park Pangandaran and the line in SMPN 1 Soccer Field Pangandaran showed the presence of sea-water intrusion that very salty with a resistance value of 0.5-2.0 ohm-meter, at a depth of 19-20 meters.

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