These faults are of high potential hazards, because they are located close to densely populated areas. Based on CSAMT data it is shown that the Lembang and Cimandiri faults are not connected to each other (Sanny 2017).

The Cimandiri active fault zone consists of six segments with a predominant sense of reverse motion (Marliyani et al. The Lembang fault was identified as a left-lateral strike-slip fault with an overall length of 29 km (Afnimar and Rasmid 2015 Daryono 2016). They are crustal, destructive earthquakes with estimated magnitudes of 8.5 and 7.0–7.7, respectively (Albini et al. Based on the historical earthquake data, large earthquakes occurred in West Java, e.g., in 17. Therefore, the western part of Java has high seismic activity (Damanik et al. The subducted Indo-Australian plate beneath the Eurasian plate along Java Island has produced some active faults in West Java, i.e., Cimandiri, Lembang, and Baribis faults and some volcanoes, i.e., Mt. West Java has a complex tectonic structure as this region is affected by the Java subduction zone and faults. While the source mechanisms of the western part of the Baribis fault indicate a thrust fault and the cluster of events in Garut shows a right-lateral slip if they are related to a local fault. The Cimandiri fault also shows a left-lateral slip, but in the south it shows a thrust fault mechanism.

Source mechanism throughout the Lembang fault indicates a left-lateral strike slip in agreement with previous studies. Histograms of travel-time residuals depict good results, in which travel-time residuals are mostly close to zero. In addition, there is another cluster in Garut trending southwest-northeast, which is possibly related to a local fault. There are several clusters of earthquakes at depths ≤ 30 km, which are probably related to the Cimandiri, Lembang, and Baribis faults. The results indicate improved hypocenter locations, where patterns of seismicity in West Java were delineated clearly. We also conducted focal mechanism analysis to estimate the type of fault slip. We then relocated the events using hypocenter double-difference method. Earthquake locations were determined using Hypoellipse code that employs a single event determination method. We determined earthquake locations through re-picking of P- and S-wave arrival times recorded by BMKG network.

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