The accurate and timely estimation of earthquake magnitude is essential for effective tsunami early warning, particularly in seismically active regions such as Indonesia. Conventional seismic approaches are often hindered by magnitude saturation in significant events (Mw > 7.5), resulting in systematically underestimated magnitudes. To address this limitation, we develop a regional peak ground displacement (PGD) scaling law using high-rate GNSS (HR-GNSS) data from 21 moderate to large earthquakes in Indonesia. Based on 87 PGD observations, we construct a regression model that relates PGD, hypocentral distance, and moment magnitude (Mw). The PGD-derived magnitudes (MPGD) exhibit strong concordance with catalog moment magnitudes, achieving a mean absolute deviation (MAD) of 0.21 and surpassing the accuracy of previously published global models. Retrospective analyses reveal that MPGD estimates converge within 2–3 min for well-recorded events and remain robust, even for great and tsunamigenic earthquakes. These results underscore the potential of HR-GNSS data to complement conventional seismic networks, providing rapid and reliable magnitude estimates for operational tsunami early warning in Indonesia.

Rapid and accurate detection of primary waves (P-waves) using high-rate Global Navigation Satellite System (GNSS) data is essential for earthquake monitoring and tsunami early warning systems, where traditional seismic methods are less effective in noisy environments. We applied a wavelet-based method using a Mexican hat wavelet and dynamic threshold to thoroughly analyze the three-component displacement waveforms of the 2009 Padang, 2012 Simeulue, and 2018 Palu Indonesian earthquakes. Data from the Sumatran GPS Array and Indonesian Continuously Operating Reference Stations were analyzed to determine accurate displacements and P-waves. Validation with Indonesian geophysical agency seismic records indicated reliable detection of the horizontal component, with a time delay of less than 90 s, whereas the vertical component detection was inconsistent, owing to noise. Spectrogram analysis revealed P-wave energy in the pseudo-frequency range of 0.02–0.5 Hz and confirmed the method’s sensitivity to low-frequency signals. This approach illustrates the utility of GNSS data as a complement to seismic networks for the rapid characterization of earthquakes in complex tectonic regions. Improving the vertical component noise suppression might further help secure their utility in real-time early warning systems.

KARAKTERISTIK LAPISAN TANAH BERPOTENSI LIKUIFAKSI BERDASARKAN RESISTIVITAS BATUAN DI DAERAH CILACAP

Relokasi hiposenter gempabumi penting dilakukan untuk mendapatkan lokasi gempabumi dengan ketelitian yang tinggi, diperlukan untuk pemetaan kerawanan gempabumi, studi struktur kecepatan, analisis seismisitas untuk studi global maupun studi lokal dan dalam analisis struktur detail seperti halnya identifikasi zona patahan dan sebaran serta orientasi patahan mikro. Salah satu teknik yang sekarang ini digunakan untuk merelokasi gempabumi adalah algoritma double difference (perbedaan ganda). Relokasi dilakukan terhadap data gempabumi BMKG yang terjadi di wilayah Jawa yang terletak pada 105°-115°BT dan 4°–12°LS. Jumlah gempabumi sebanyak 1352 kejadian. Jaringan stasiun pencatat yang dipergunakan sebanyak 47 buah. Hasil relokasi menunjukkan pergeseran hiposenter lebih dari 50 km sebanyak 7 gempabumi. Pergeseran hiposenter menyebar ke segala arah dan tidak memiliki kecenderungan ke arah tertentu, namun demikian perubahan hiposenter terbanyak ke arah barat. Relokasi gempabumi dengan kedalaman awal 10 km menunjukkan pergeseran yang random. Relokasi menggunakan hypoDD menunjukkan peningkatan kualitas bila dilihat dari distribusi residual. Relocation of earthquake hypocenter is important for obtaining an very accurate earthquake location which is needed for mapping of earthquakes vulnerability, velocity structure study, global and local studies of seismicity analysis and detail structural analysis as well as identification of the fault zone, distribution and orientation of microfracture. One technique currently used to relocate earthquakes is double difference algorithm. Relocation performed on BMKG earthquake data that occurred on Java region, located on 105°-115°E and 4°-12°S. The total number of earthquakes are 1352 events. We used 47 recording station networks. Hypocenter relocation results showed 7 earthquakes shift more than 50 km. Shift in hypocenter spread in all directions and do not have a tendency, however, most hypocenter changes to west. Relocation of initial depth 10 km earthquakes showed random shifst. Relocation using hypoDD showed an increase in quality when viewed from the residual distribution.

Accurate and timely earthquake magnitude estimation is critical for effective tsunami early warning, particularly in seismically active regions like Indonesia. Conventional seismic approaches often suffer from magnitude saturation for large events (Mw > 7.5), leading to underestimated magnitudes. To address this limitation, we propose a novel Peak Ground Displacement (PGD) Scaling Law based on regional high-rate GNSS (HR-GNSS) data from 21 moderate to large Indonesian earthquakes. Using 87 PGD measurements, we derive a regression model that relates PGD, hypocentral distance, and moment magnitude (Mw). The PGD-derived magnitudes (MPGD) show strong agreement with final moment magnitudes (Mw), achieving a mean absolute deviation (MAD) of 0.21—outperforming global models. Retrospective analyses demonstrate that the PGD estimates stabilize within 2–3 minutes for well-recorded events and remain robust even for great and tsunamigenic earthquakes. These findings confirm that HR-GNSS data can complement seismic networks, enabling rapid and reliable magnitude estimation in Indonesia.

Indonesia has a high level of seismic vulnerability because located in the junction area of four large plates, namely the Eurasian plate, Indo-Australian plate, Pacific plate, and Philippine Plate, and also the number of active faults that stretch throughout its regions. One of the efforts to mitigate earthquake disasters is to conduct seismic hazard microzonation efforts. The Research and Development Center of BMKG has carried out ongoing research in the field of seismic microzonation to obtain information on the level of seismic hazard in some regions based on microtremor parameter values, including in the Sukabumi (2009), Bantul (2010), Padang (2011), Cilacap (2012), Kulonprogo (2014), Tasikmalaya (2017), Garut (2018) and Pangandaran (2019). This study tries to prototype the seismic microzonation information system in a web-based spatial information system called InaSMIS (Indonesia Seismic Microzonation Information System). InaSIMS contains information about the analysis of microtremor survey results, including the value of the dominant period (T0), Ground Shear Strain (GSS), and USGS Vs30, which states the level of seismic hazard in an area. InaSMIS is still being developed in the research stage and is not yet an operational service for BMKG. In the future, InaSMIS expected to be a source of public information to determine seismic hazards in Indonesian regions.