The Central Java region is one of the most seismically active regions in Indonesia. Each year, the region experiences an average of more than 20 medium-tolarge magnitude earthquakes. Hence, reliable hazard analysis is necessary for the region, and we undertook this study in order to conduct a probabilistic seismic-hazard analysis to estimate and map peak ground acceleration (PGA) and spectral response at 0.2 and 1 s periods, with 10% probability of exceedance in 50 years corresponding to the return period of 475 years. Maps presented in this study are intended for regional purposes only and may be useful for emergency response planning and urban development. The database used in this study is compiled from the Indonesian Meteorological, Climatological, and Geophysical Agency, the U.S. Geological Survey, and the Incorporated Research Institutions for Seismology. The compiled catalog covers an area between latitude 5°-12°S and longitude 105°-115°E and includes moment magnitude 5 and greater from 1900 to February 2011. We used a standard logic-tree approach that included systematic allowances for various seismicity models. Because a region-specific empirical ground-motion model is lacking, we used Next Generation Attenuation ground-motion relations. We calculated PGA and spectral response at 0.2 and 1 s periods for all cities across Central Java. We found that the city of Pati is subject to the highest seismic hazard with a PGA of 0:45g, and the city of Kendal has the lowest hazard with a PGA of 0:13g. This study provides a basis upon which to design maps for building codes and emergency planning.

The study was conducted to determine the response of the Semarang Coastal area to eartquakes by measuring the micro tremor response with 3 component seismographs at 110 locations on the Semarang coastal region that were distributed almost evenly. From the micro tremor data, it is processed using Gyopsy software to get the dominant frequency and amplification values. The dominant frequency value and its amplification are then made a map with surfer 13, and the results are then overlaid on the RBI map for qualitative interpretation. The results of this study are dominant frequency and their amplification in the Semarang coastal region maps. The dominant frequency values range from 0.5 Hz - 10 Hz. Based on the dominant frequency values, can be grouped into three categories, namely low frequency values that are less than 2.5 Hz associated with sediment thickness values of more than 30 m and areas with moderate frequencies with values between 2.5 - 4 Hz associated with sediment thickness 10 - 30 m, and high frequency indigo between 4 Hz - 10 Hz is associated with a sediment thickness of 5-10 m. Areas with low frequencies dominate the study area. Areas with medium and high frequency values are only a small part of the study area. The amplification values vary between 0.5 - 8.5. While the amplification value can also be grouped into 3 parts, namely the amplification of less than 2.75 associated with hard rocks almost dominates the central part of the study area, the amplification value between 2.75 - 5.15 associated rocks or soil with moderate violence is only a small part as between low and high values in the study area, and values of more than 5.15 associated with soft soils that dominate the northern and the southern part of the study area.. If the area around Semarang has an earthquake, the location with a large amplification will be more prone to earthquake disasters.

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The presence of oil seepage to the surface indicates that at least an active petroleum system is present subsurface. Oil seepage that occurred in Plantungan, Kendal, Central Java, has been known since 1971 and still produces seepage until today. On the research area, three oil seepages point were found. Plantungan region is located in East Serayu Zone underlain by volcanic area, and based on the Geology Map, the research area is located in Banjarnegara-Pekalongan Sheet. To understand the geology condition of the research area, a subsurface mapping is needed, even though the mapping does not provide the depth of bedrock and reservoir, data recording using HVSR (Horizontal to Vertical Spectrum Ratio) method that has been done in 18 points is able to provide Vp and density profile to understand the distribution of oil seepage. The oil seepage is most prominent close to SB09 location, however the result from crossplot found that the value of highest Vp×density is on SB12A with 4,306,197 kg/m2s, and lowest Vp×density in on SB17A with 302,305.3 kg/m2s.

Geothermal system requires specific geological condition that allow deep circulation of ground water to extract heat from the heat source. Faults and fractures play a major role in the localization and evolution of hydrothermal flow on several scales. The research aim was to obtain the permeability pattern of hydrothermal fluid base on response of micro seismic waves to subsurface structures. In one dimensional structure, average Horizontal to Vertical (H/V) spectral ratios can be assumed to measure the ellipticity of fundamental mode Rayleigh wave. Hence the shape of H/V ratios can be used to estimate the shear-wave velocity profile. The poisson’s ratio value of the hot spring corresponds to the physical properties of rock containing fluids. The thickness of the sand deposit and the soft layer indicated in the hot spring zone. We interpreted that we have warm springs in the research area comes up by the fracture or fault zone and permeable zone of sand soil. The mixing waters flow to the earth’s surface through the structure.