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This research aims as one of the efforts to mitigate earthquake disasters by using the HVSR method based on microtremor data at 28 BMKG seismic stations in the central Java Island region to estimate the dominant frequency (f0) and amplification (A0) that describe the dynamic characteristics of the soil and analyse the shear wave velocity at a depth of 30 meters (Vs30). The dominant frequency values in the study area range from 0.648 to 18.257 Hz. The amplification values scattered in the study area ranged from 0.788 - 7.496. This research also produces dominant period parameters (T0) and seismic vulnerability (Kg). The highest seismic vulnerability values are at BUJI in Buayan, Kebumen; GBJI in Gringsing, Batang; and SBJM in Sanden, Bantul. In addition, the Vs30 value is helpful to determine how strong the building foundation resists earthquakes. Based on the Vs value in the ground profile with ellipticity curve modelling, the Vs30 value ranges from 204.756 - 903.046 m/s. The distribution of Vs30 values shows that the research points in central Java are spread by a variety of hard and very dense soil types to soft rock (SC).

Sumatra Island and its surroundings, Indonesia, are one of the most active tectonics in the world. The Aceh-Andaman earthquake, one of the most destructive earthquakes in the world, occurred there. It has attracted many earth scientists to apply various methods, including seismic tomography, to understand the island’s subsurface structure and tectonic system. This study is the first to delineate subsurface imaging beneath the island and its surroundings using a local-regional earthquake catalogue from the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) seismicnetwork. The tomographic imaging of P-wave (Vp) conducted in this study has successfully delineated subduction slabs (high Vp), partial melting zones (low Vp), volcanic arcs (low Vp), and Sumatran Fault zones (low Vp). The relationship between the subduction zone and the volcanic arc on the island can be seen on several vertical sections where a partial melting zone occurs at a depth of about 100 km, which functions as magma feeding for some volcanoes on the island. The oceanic slab model also exhibits a more pronounced and steeper slope towards the southern regions of Sumatra Island, possibly attributed to the slab’s aging process in that direction. The results highlight the importance of the BMKG seismic network in imaging local-regional subsurface structures beneath Indonesia’s archipelago, especially for the main islands such as Sumatra.

The tsunami of Sunda Strait occurred on December 22, 2018, at 21:03 West Indonesia Time (zone). An eruption of Mount Anak Krakatau caused an eruption that triggered a landslide on the slopes of Mount Anak Krakatau covering an area of 64 hectares that hit the coastal area of western Banten and southern Lampung and resulted in 437 deaths, 14.059 people were injured, and 33.721 people were displaced. Before the tsunami, signal transmissions (gaps) at the Lava seismograph station installed on the body of Mount Anak Krakatau experienced broken so that Mount Anak Krakatau Observation Post could not record volcanic earthquake signals since December 22, 2018, at 21.03 West Indonesia Time (zone). Given these facts, proper monitoring and analysis were required to monitor and analyze the source of ground vibrations originating from the eruption of Mount Anak Krakatau. Therefore, this study aims to confirm the eruptive activity of Mount Anak Krakatau based on seismic monitoring and analysis sourced from the BMKG's seismic sensor network. The method the author uses is by monitoring the seismic signal recorded by the seismometer and analyzing the seismic signal using the Seiscomp3 software. By the results of monitoring and analysis of seismic data, it was found that the location of the center of the ground shaking was on Mount Anak Krakatau with a magnitude of 3.4, and a depth of 1 km. To anticipate similar tsunami events in the future, it is very necessary to have a tsunami early warning system originating from volcanic activity and volcanic body avalanches.

The Horizontal to Vertical Spectral Ratio (HVSR) is a seismic analysis method used to obtain information about subsurface geological characteristics. This method is based on the spectral ratio analysis between the horizontal and vertical components of earthquakes or other vibration sources. HVSR has proven to be an effective tool in evaluating rock layers, layer thickness, rock hardness, and geological hazard potential. In the HVSR method, seismic data are measured using three-component seismometers, the N-S (North-South), E-W (East-West), and vertical components. In this study, the HVSR method is used for Vs30 inversion to estimate shear wave velocity at a depth of 30m. The southern and western regions of Sulawesi have various geological conditions and high seismicity levels. The results of this inversion can be used for mapping soil vulnerability indices. The obtained soil vulnerability index values indicate high vulnerability near the Palu-Koro fault, with A0 9.27 at F0 3.2 Hz. This method can also estimate shear wave velocity values at a depth of 30 m. Vs30 values range from 200 m/s to 500 m/s at various measurement points, indicating variability. According to the SNI 1726:2012 and NEHRP classifications, the research area has soil conditions ranging from medium to soft.

The island of Borneo has relatively low seismic activity. However, the plan to relocate the capital city to the East Borneo region could potentially increase the population, making the area more vulnerable to earthquake occurrences. Therefore, this research aims to determine the depth of the Mohorovičić discontinuity layer, which will provide insights into the thickness of the Earth's crust, and model the local P and S wave velocities using the Inversion, Migration, and Stacking H-k methods. The data used consists of earthquake events with magnitudes greater than 6, located within a distance of 30° to 90° from 6 BMKG stations around the new capital of Indonesia. The research results indicate that the depth of the Mohorovičić discontinuity layer varies between 28 and 43 km. The model of P-wave velocities varies between 1.8 km/s to 9.1 km/s, while the model of S-wave velocities ranges from 1.0 km/s to 5.1 km/s.

Seram Island is the northern part of the Banda subduction which is characterized by the existence of a thrust fault structure in the Seram Trough as the main contributor to seismicity in this region. Complex tectonic activity also forms a deformation zone of the Kawa Fault with a sinistral strike slip mechanism and high-angle normal faults in the mainland. On June 16, 2021 a Mw 6.0 earthquake occurred on the south coast of Seram, in Tehoru to be precise, which followed by a small tsunami wave which is thought to have been generated by an underwater landslide. This earthquake has a normal fault mechanism which is quite rare on Seram Island, however, the actual fault plane that caused the earthquake is still unknown. In this study, we investigate potential faults that may have caused the 2021 Tehoru earthquake by performing a seismicity analysis using well relocated hypocenter of the mainshock and the aftershocks sequence. We use the double-difference relocation method with the SVD algorithm performed in the hypoDD program. The results show the distribution of aftershocks that form a northeast-southwest trending lineation. The depth of the hypocenter has also improved from being dominated by fixed depth to being varied with dominance at depths of 8-14 km. An important feature of the relocation results is that the aftershocks distributed downward along a ~35° northwest-dipping plane which indicates a southwest-northeast fault orientation. This result confirmed by using geodetic observations that shows a horizontal displacement of 14 mm toward northwest direction and a land subsidence of 14 mm. This southwest-northeast oriented fault structure is thought to be associated with high-angle normal fault resulting from a north-south extension activity in the central part of Seram Island. The results of this study indicate the existence of other local fault structure in the Seram Island which can be used as a basis for seismic hazard assessment, other than seismic activities from Seram Trough and Kawa Fault.

Spatial interpolation methods, such as Inverse Distance Weighting (IDW) and kriging, are commonly used in various fields. In Kriging method, semivariogram fitting is an important step, where empirical data are used to derive a theoretical model. However, when the known theoretical semivariogram model does not provide a satisfactory fit, the bias in the estimated values is increased. To address this limitation, Support Vector Regression (SVR) can be used to model the empirical semivariogram with a machine-learning method. This method has been applied in ordinary kriging interpolation for semivariogram fitting to estimate parameters related to the potential occurrence of earthquake. Specifically, the calculated parameters, based on the Gutenberg-Richter law, include the seismic activity (a-value) and rock fragility (b-value) in the Sumatera region. The results showed that SVR can model the empirical semivariogram better than the theoretical. The integration of SVR-Ordinary Kriging provides the best performance compared to other methods, such as IDW, with the smallest RMSEP values for both the b-value and a-value measuring 0.1378 and 0.7423, respectively. Aceh and Mentawai Islands tend to show low a and b values, suggesting that these areas are more vulnerable to earthquake with large magnitudes.

The Sunda Strait lies between two distinct tectonic regions with perpendicular and oblique subduction in Java and Sumatra, respectively. The region experiences significant seismic activity, with an active volcanic ring resulting from the collision between the Indo-Australian and Eurasian plates. In this research, we employed 3-D velocity tomography to visualize the subsurface in the western Java region, particularly within the Sunda Strait, down to a depth of 150 km. We utilized traveltime data for P- and S-waves from 1,418 earthquakes with at least 15 phases and magnitude greater than M3, which were recorded at 52 the Indonesian Agency for Meteorology, Climatology, and Geophysics (BMKG) seismic stations between April 2009 and December 2021. We used the SIMULPS12 code to simultaneously invert the velocities of P- and S- waves, the Vp/Vs ratio, and the hypocenter locations. High- and low-velocity anomalies from seismic tomography may depict geological features such as the subduction slab, volcanism, and other seismogenic zones. Our results show that high-velocity anomalies indicate the curvature of the oceanic slab subducted below the region extending from Western Java to Southern Sumatra, a low Vp/Vs ratio, and clustered seismicity down to 150 km depths. We suggest the presence of partial melting zones at 100 km depth beneath Mount Sekincau, Krakatau, Prakasak, and the Mount Salak and Guntur complexes, which are indicated by low velocity and high Vp/Vs ratio.

The aim of our study was to identify the genetic and phylogenetic characteristics of spiny lobster Panulirus versicolor in Cendrawasih Bay, Indonesia and their relationship with P. versicolor lobsters elsewhere in several Pacific and Indian Oceans domains based on the cytochrome oxidase I (COI) gene. We collected tissue samples from five P. versicolor individuals in Cenderawasih Bay. We detected that there were 5 haplotypes with a diversity value of haplotype (Hd) and nucletides (Pi) respectively Hd = 1.000 and nucleotides Pi = 0.00841. Our data show that some P. versicolor individuals from Cenderawasih Bay were closely related to P. versicolor lobsters in other regions of the Indian Ocean and the western Pacific Ocean. We observed the P. versicolor of Cenderawsih Bay form a monophyletic clade with P. versicolor in other part of the Indian Ocean and the western Pacific Ocean based on the reconstruction of phylogenetic trees. As well as the haplotype distribution showed no sample area genetically isolated from the others.