Wahyu Hidayat

We present a hypocenter relocation analysis to examine the distribution of seismicity in the Central Java and Yogyakarta regions in Indonesia. The data were obtained from the BMKG earthquake database for the period August–October 2024, covering the area between 6.0˚–11.0˚ S and 108.5˚–111.6˚ E. The dataset was divided into three monthly groups to observe the spatial and temporal patterns of earthquake sources in the study area. The analysis was carried out by overlaying the relocated hypocenters onto active fault maps and the subduction pattern of southern Java, allowing for a clearer characterization of the earthquake sources. Data from August - October 2024, comprising 393, 424, and 276 earthquake events respectively, were analyzed using the Double - Difference relocation method based on 26,610 - 19,429 P-wave pairs and 21,447 - 15,933 S-wave pairs recorded by 28 seismic stations. The findings reveal significant activity along the Baribis - Kendeng Fault, Kebumen - Meratus Trend, and Progo - Muria Lineament, exhibiting diverse fault mechanisms and hypocenter depths from shallow to intermediate. Clustering near the Opak Fault Zone and associated structures indicates complex fault interactions with potential intersegment stress transfer, while offshore seismicity shows a steeply dipping subduction slab with intermediate- to deep-focus events (50-250 km). The combined occurrence of shallow crustal, intermediate, and deep intraslab earthquakes expands the regional hazard spectrum, highlighting risks of strong ground shaking, site amplification, and localized tsunamis. The findings highlight the importance of integrating multisource and multimechanism earthquake characteristics into probabilistic hazard models to improve spatial planning, infrastructure resilience, and community preparedness.

Scientific publication is one of the primary indicators of academic quality and institutional reputation in higher education. This article discusses strategies and the implementation of enhancing scientific publications in the Geophysical Engineering Study Program as part of the effort toward international accreditation. The research method employed is a case study with a qualitative-descriptive approach through interviews, questionnaires, document analysis, and observation of academic activities. The findings indicate that the main challenges in publication include limited writing skills, a lack of global collaboration, and the high workload of the three pillars of higher education (teaching, research, and community service). Key success factors for publication are research data quality, academic writing skills, and access to international references. This article proposes strategies such as writing workshops, mentoring systems, strengthening collaborations, providing incentives, and improving research infrastructure. Implementing these strategies not only increases the quantity and quality of publications but also strengthens the study program’s position in achieving international recognition.

Mining-induced seismicity has become a significant concern in deep underground mining, primarily due to the increasing depths of extraction and the complex stress conditions. Significant seismic events are often followed by aftershock sequences that pose significant risks to worker safety and mine infrastructure, highlighting the importance of reliable aftershock identification and exclusion zone determination for re-entry protocols. The goal is to enhance the accuracy of aftershock identification resulting from underground mining activities and minimize noise in microseismic catalogs, thereby supporting mine safety. This study applies the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm to a synthetic microseismic catalog of 1471 events with moment magnitudes ranging from-1.6 Mw to 2.5 Mw. After magnitude of completeness (Mc) filtering, DBSCAN was used to spatially cluster aftershocks, effectively distinguishing them from background seismicity and noise. Results show that large sequences, such as the moment magnitude event 2.5 Mw with 1,471 aftershocks, were reduced to 1,015 clustered events. The clustered events show a more precise spatial concentration than the original distribution, which makes it simpler to tell which aftershocks are related to the mainshock and which are not. Before clustering, the catalog had 1,471 aftershocks for each mainshock with a maximum magnitude of 2.5 Mw. After clustering, 1,015 aftershocks were correctly identified as part of the sequence cluster.

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

The block caving mining method has become increasingly popular in the last two decades. Meanwhile, Indonesia has several potential ore bodies which have not yet determined suitable mining methods. The references to block caving mining projects worldwide and the potency of metal deposits in Indonesia were reviewed to determine the requirements of ore bodies suitable for mining using the transformed block caving method. This method can be applied on a blocky ore body with a thickness of 200–800 m, various rock mass strengths until 300 MPa, from low to high (from 0.3% Cu until more than 1.0% Cu), but of uniform grade and at a depth from 500 to 2200 m. The technical specifications for running block caving mines have been synthesized, including preparation methods, undercutting strategy, mine design, mining equipment and monitoring. Considering the requirements and the successful practice of the block caving project in the Grasberg Caving Complex as a role model, the Indonesian government should concentrate on the detailed exploration of porphyry deposits and feasibility studies on applying the method to the prospective ore bodies, i.e., Onto, Tambulilato, Tumpangpitu and Randu Kuning. In addition, the exploration method, cost, operation, environment, mining policy and social geology are important aspects worth noting.

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.