In the last two years two earthquakes occurred and caused some damages to buildings in Pangalengan (2016) and Garut (2017) regions. In this study, we have conducted hypocenter determination with high accuracy and focal mechanism analysis of the two events to estimate the type of fault slip. We have determined the earthquake locations through re-picking of the P- and S-wave arrival times recorded by the BMKG seismic network in West Java. Earthquake locations have been determined using the Hypoellipse codes that employ a single event determination method. Both of these earthquakes are indicated as a result of an unidentified fault (we name it as GARSELA fault), which has a southwest-northeast trending direction. The focal mechanism solutions for these two events show a strike-slip fault type and normal fault type, respectively. Based on our previous study, this fault has also a high seismicity activity (small events). It is suggestive that the recent two events indicate that GARSELA is an active fault.

In the case of mining in an inclined intrusion using the block caving method, the highest stress is usually concentrated in the seismogenic and abutment zones, especially in the front of the sloping area. In an inclined intrusion of more than 40°, the seismometer network is usually distributed in the facility area where the footwall area is also located. This causes a limitation in microseismic monitoring due to ray coverage. In this study, we conduct a seismometer deployment outside a mining facilities area with borehole seismometers. The study aims to maximize the resolution and minimize the monitoring uncertainty of underground mines. We created two scenarios of seismometer deployment: (i) seismometers are deployed following the intrusion mining level in the mining facility area; and (ii) additional seismometers are deployed in off-facilities areas. Both areas were tested for their raypath responses and sensitivity using the Checkerboard Resolution Test (CRT). The monitoring resolution influenced by the additional borehole seismometers in the off-facilities area can be quantified. The results suggest that the additional seismometers in the off-facilities areas can increase resolution by 30% in the seismogenic and abutment zones.

Caving activity results in an increased induced seismicity which should be monitored to avoid massive and uncontrolled rock damage. This research was conducted at the Deep Mill Level Zone (DMLZ) underground mine, the deepest underground mine in Indonesia operated by PT Freeport Indonesia. This research aims to monitor cave propagation by using 4D tomography with a catalogue of microseismic for 57 days with a total of 14,821 events recorded by 84 stations consisting of 176,265 P phases and 133,472 S phases. The data is divided into four subsets to see the velocity evolution related to cave progress. Checkerboard Resolution Test (CRT) and Derivative Weight Sum (DWS) are used to assess the resolution of the inversion. 3D initial velocity model is constructed based on geological information and coring data. We have succeeded in identifying the interpreted cave propagation of a 60 m extension to the NW at around 100 m above undercut level based on 4D changes in velocity tomogram validate by Time Domain Reflectometry data. The decrease of Vp and Vs in subset 3 is interpreted due to the fracturing processes as the cave progresses. Furthermore, we observe a stress redistribution along with the progress of the cave, which is characterized by high velocities (Vp and Vs) due to compensation for changes in low velocity values ​​in the area in front of the cave, which is starting to collapse. We suggest that a considerable change in the velocity tomogram as an indicator of impending caving.

Seismic tomography is a method that is widely applied to obtain seismic velocity structures below the surface. This method is applied to various cases, from glo Seismic tomography is a method that is widely applied to obtain seismic velocity structures below the surface. This method is applied to various cases, from glo

Many aspects of earthquake mechanics remain an enigma, e.g.: earthquake interaction and seismic hazard mitigation. One potential bright spot is the finding that simple calculations of stress changes may explain some earthquake occurrences and interactions. This progress is especially lead by abundant studies of stress changes of human-induced seismicity. This work introduces stress triggers, stress shadows, and their implications for seismic hazard in Indonesia. We review our work on stress analysis of the 2016 Aceh earthquake and present a compilation of quantitative earthquake interaction studies from a stress change perspective. The 2016 earthquakes were deadly, caused more than 100 causalities, and unpredicted, in a sense that the driving force and the source mechanism remain unclear. No information was present on the extent of the faulting or the direction of propagation of the event. Therefore, it requires a stress transfer modeling in order to understand the possible seismic hazard distribution. The results of this study provide some clues about certain aspects of earthquake mechanics. It also demonstrates that we still have a lot of work ahead of us before we can understand the complete mechanism of how an earthquake occurs.