Penjalaran Tsunami Menuju Ke Outlet Arlindo Berdasarkan Skenario Gempa Megathrust Selatan Jawa

Dari hasil relokasi kejadian gempa yang tercatat oleh Badan Meteorologi, Klimatologi, dan Geofisika (BMKG) dan inversi data Global Positioning System (GPS) menunjukkan bahwa terdapat celah seismik (seismic gaps) di selatan Jawa, yaitu wilayah di sepanjang batas lempeng aktif yang tidak mengalami gempa besar atau gempa selama lebih dari 30 tahun. Pada zona tersebut diperkirakan terjadi penguncian (locked) terhadap pergeseran lempeng (slip deficit) yang berakibat pada akumulasi pengumpulan energi dan berpotensi menimbulkan gempa megathrust yang bersifat tsunamigenik. Pada penelitian ini dilakukan pemodelan numerik tsunami menggunakan persamaan gelombang shallow water 2 dimensi dengan 3 skenario gempa megathrust akibat patahnya lempeng samudera di zona celah seismik selatan Jawa. Skenario patahan lempeng di selatan Jawa Barat menyebabkan gempa dengan Mw 8,9, di selatan Jawa Tengah dan Jawa Timur sebesar Mw 8,8, dan untuk skenario patahan dari Jawa Barat sampai Jawa Timur sebesar Mw 9,1. Dari hasil simulasi selama 10 jam menggunakan software TUNAMI N2, dihasilkan gelombang tsunami setinggi maksimum 6 meter di pesisir selatan Jawa untuk gempa berkekuatan Mw 8,9, 12 meter untuk gempa berkekuatan Mw 8,8, dan 20 meter untuk gempa berkekuatan Mw 9,1. Propagasi dan travel time tsunami diamati oleh outlet-outlet ARLINDO berupa shallow pressure gauge (SPG) yang ditempatkan di jalur-jalur ARLINDO.

Experimental study of the seismic performance of plasterboard partition walls with seismic gaps

It is now widely recognized that the performance of non-structural elements is crucial to the performance of building systems during earthquakes. Field surveys and experimental studies have shown that light steel or timber framed plasterboard partition walls are particularly vulnerable. The objective of this study is to investigate the seismic performance of a novel seismic gap partition system with angled return walls under quasi-static cyclic loading applied obliquely and to investigate the benefits of using acrylic gap-filler in the seismic gaps. Two specimens were tested: a steel stud specimen and a timber stud specimen. Observed drift capacities were significantly greater than traditional plasterboard partition systems. Equations were used to predict the drift at which damage state 1 (DS1) and damage state 2 (DS2) would initiate. The equation used to estimate the drift at the onset of DS1 accurately predicted the onset of plaster cracking but overestimated the drift at which the gap filling material was damaged. The equation used to predict the onset of DS2 provided a lower bound for both specimens and also when used to predict results of previous experimental tests on seismic gap systems. The gap-filling material reduced the drift at the onset of DS1, however, it had a beneficial effect on the re-centring behaviour of the linings. Out-of-plane displacements and return wall configuration did not appear to significantly impact the onset of plaster cracking in the specimens.

Correlation Dimension and Seismic Quiescence around Northern Sumatra

The implementation of the correlation dimension (Dc) analysis is often used to measure the scaling attribute's possible size or grouping of seismotectonic variables. Related to seismicity in certain areas, Dc can suggest the existence of potential seismic gaps to release strain energy in the future. It can be identified that the presence of earthquake precursors can be characterized by changing the pattern of seismicity in space-time correlate strongly with the existence of zones and periods of seismic quiescence before major earthquake events. In this study, the Dc and the difference of Dc (δDc) are evaluated based on previous studies in which Dc is estimated based on the b-value of shallow earthquake data, and δDc is calculated based on the two periods before and during Region Time Length. We found the consistency that the areas filled by large earthquake events are in the zone with relatively high Dc and δDc. Dc tends to have a strong correlation to suggesting the existence of potential seismic gaps to release strain energy. δDc could be correlated with the possible stress transfer that may trigger the next sequence large earthquake.

Implications for megathrust earthquakes and tsunamis from seismic gaps south of Java Indonesia

Relocation of earthquakes recorded by the agency for meteorology, climatology and geophysics (BMKG) in Indonesia and inversions of global positioning system (GPS) data reveal clear seismic gaps to the south of the island of Java. These gaps may be related to potential sources of future megathrust earthquakes in the region. To assess the expected inundation hazard, tsunami modeling was conducted based on several scenarios involving large tsunamigenic earthquakes generated by ruptures along segments of the megathrust south of Java. The worst-case scenario, in which the two megathrust segments spanning Java rupture simultaneously, shows that tsunami heights can reach ~ 20 m and ~ 12 m on the south coast of West and East Java, respectively, with an average maximum height of 4.5 m along the entire south coast of Java. These results support recent calls for a strengthening of the existing Indonesian Tsunami Early Warning System (InaTEWS), especially in Java, the most densely populated island in Indonesia.