<p>A tsunami numerical inundation modeling in the Ambon city was developed by considering large earthquakes along the Ambon bay strike-slip fault and triggering submarine landslide as the tsunami source.&#160;<br>The simulation was conducted using Comcot (Cornell Multi-grid Coupled Tsunami model) with a nested grid system in the spherical coordinate system. The four different spatial grid sizes of 60 (layer 1), 15 (layer 2), 3.75 (layer 3), and 0.9375 (layer 4) arc-sec were used in the computation. The linear shallow-water theory with bottom friction was applied for layers 1 -3, meanwhile, layer 4 used the non-linear shallow-water theory with manning roughness coefficient and detail bathymetry data.&#160;<br>The single segmentation of earthquake scenarios with magnitudes Mw 7.2 was assumed. The earthquake then triggers submarine landslides in some areas around Ambon city. The landslide area was approached by Peak Ground Acceleration (PGA) value and historical data.<br>The results showed that in Ambon city the first tsunami wave arrived 18 min after the earthquake with a maximum flow depth of 7.4 m and inundation distance around 1.2 km. These results show that Ambon city has a risk of tsunami threat from earthquakes and submarine landslides. Therefore, it is necessary the tsunami hazard preparedness by the government and communities.</p>
Abstract Shear-wave splitting (SWS), or the propagation of two independent shear waves, can be used as an indicator of seismic anisotropy. In this study, we utilize this concept using aftershock data of the 2018 Lombok earthquake which had been acquired in period of August 4 – September 9, 2018. The goal of this research is to better understand the crack distribution related to the rupture zone of the 2018 Lombok earthquake. After applying instrument correction to the data, the waveform data were then windowed in each P and S arrival time. To determine the SWS parameters, we performed rotation in each horizontal seismogram components. The horizontal components were rotated from azimuth 0° to 180° with an increment of 1°. Cross-correlation coefficient (CCC) was determined for each rotation angle. The polarization direction and the SWS delay time were chosen from the parameters shown in the highest value of CCC.
<p>The Central and East Java region is part of the Sunda Arc which has an important role in producing destructive earthquakes and volcanic complexes as a result of the subduction of the Indo-Australian plate under the Eurasian plate. Seismic tomography is one geophysical tool that is adaptable to understanding the mechanism process related to tectonic activity, seismicity, and volcanism. We collected a series of waveforms from 1,519 events in the period January 2009 to September 2017 and re-picked 11,192 phases for P- and S-waves at 34 stations of the BMKG network. We determined the 3-D P- and S-wave velocity structure beneath this high-risk region down to a depth of 200 km. In this study, we compare the tomographic images and relocated seismicity in order to represent the subducted slab geometry and the features in the seismic zones, i.e. the 2006 Yogyakarta earthquake zone (Opak fault), south of the mainland, and the 1994 Banyuwangi earthquake zone. Low-velocity anomalies beneath the volcanoes, i.e. Merapi, Merbabu, Kelud, Semeru, Bromo, and Ijen also imply the existence of fluid material and possible partial melting of the upper mantle which migrated from the subducted slab.</p>
Uji resolusi dalam tomografi seismik telah diterapkan secara luas pada berbagai skala. Uji tersebut digunakan untuk mengetahui kehandalan data seismik yang digunakan pada suatu area penelitian. Checkerboard resolution test (CRT) merupakan salah satu teknik uji resolusi yang diterapkan secara luas pada data tomografi seismik. Uji resolusi dilakukan untuk mengetahui secara spasial area mana saja yang bisa diinterpretasi dari suatu tomogram seismik. Pada penelitian ini akan menguji resolusi dengan input model CRT dan Non-CRT. Area yang memiliki kemiripan pola antara input model dan hasil inversinya menunjukkan area tersebut bisa diinterpretasi baik secara geologi maupun dari properti fisika batuannya. Pada uji resolusi model Non-CRT juga ditambahkan random noise untuk mengetahui sejauh mana pengaruh noise terhadap data seismik. Hasil uji resolusi pada kedua input model tersebut menunjukan konsistensi pada area-area yang bisa diinterpretasi ataupun tidak. Hal ini menunjukkan data seismik yang digunakan pada penelitian ini memiliki kualitas yang cukup baik sehingga hasil studi tomografinya bisa menjelaskan kondisi geologi di bawah permukaannya
An update version of 3-D Shear Wave Velocity (Vs) & Crustal Interface (Sediment Basement & Moho) Models of Borneo, Makassar Strait and Sulawesi region obtained from group velocity tomography. Group velocity is retrieved from dispersion analysis of Rayleigh waves extracted from the ambient noise field by cross-correlating long-term recordings from 108 seismic stations over a period of 8 months. A 3-D shear wave velocity model then are produced via a two-stage process in which group velocity maps are computed across a range of periods and then sampled over a dense grid of points to produce pseudo-dispersion curves; these dispersion curves are then separately inverted for 1-D shear wave velocity (Vs), with the resultant models combined and interpolated to form a 3-D model.
Gempa Bantul 27 Mei 2006 (M=6,4) menyebabkan kerusakan parah dan menelan korban jiwa
sangat besar di zona Graben Bantul, Yogyakarta. Timbulnya kerusakan akibat gempa dengan
sebaran yang tidak merata sangat menarik untuk dikaji. Penelitian ini bertujuan menganalisis
hubungan antara indeks kerentanan seismik, shear-strain ground, dan rasio kerusakan pada
setiap satuan bentuklahan. Penelitian ini menggunakan pendekatan spasial dengan satuan
bentuklahan sebagai satuan analisis. Teknik pengambilan data mikrotremor menggunakan
proportional purposive sampling. Analisis data mikrotremor menggunakan Metode
Horizontal to Vertical Spectrum Ratio (HVSR). Hasil penelitian menunjukkan bahwa nilai
indeks kerentanan seismik 1,0 - 23,21 tersebar pada satuan bentuklahan Dataran
Fluviovulkanik Merapi Muda, Dataran Kaki Vulkanik Merapi Muda, Lereng Kaki Koluvial
Perbukitan Baturagung, Kompleks Beting Gisik dan Gumukpasir, dan Dataran Fluviomarin.
Indeks kerentanan seismik kurang dari 1,0 terdapat pada seluruh satuan bentuklahan
perbukitan struktural, seperti satuan bentuklahan Perbukitan Struktural Formasi Sentolo,
Perbukitan Struktural Nglanggran, Perbukitan Struktural Kebo, Butak, dan Semilir. Nilai ratarata ground shear-strain paling besar terdapat pada satuan bentuklahan Dataran
Fluviovulkanik Merapi Muda (γ=3.402×10-6) sedangkan rata-rata ground shear-strain paling
kecil terdapat pada satuan bentuklahan Perbukitan Struktural Formasi Sentolo (γ=36×10-6).
Nilai rasio kerusakan paling besar terjadi pada satuan bentuklahan Dataran Fluviovulkanik
Merapi Muda (R=75,3%), dan rasio kerusakan rumah paling kecil terjadi pada satuan
bentuklahan Perbukitan Struktural Formasi Sentolo (R=12,0%). Karakteristik indeks
kerentanan seismik berdasarkan mikrotremor, ground shear-strain, dan rasio kerusakan
berubah mengikuti satuan bentuklahan. Persebaran kerusakan akibat gempa Bantul 27 Mei
2006 yang terkonsentrasi di zona Graben Bantul merupakan fenomena efek tapak local (local
site effect) akibat tingginya nilai indeks kerentanan seismik pada Dataran Fluviovulkanik
Merapi Muda dan Dataran Kaki Vulkanik Merapi Muda.
Kata kunci: indeks kerentanan seismik, ground shear-strain, rasio kerusakan, satuan
bentuklahan, graben, HVSR
Abstract The island of Lombok in Indonesia is located between the Indo-Australian and Eurasian subduction trenches and the Flores back-arc thrust, making it vulnerable to earthquakes. On 29 July 2018, a significant earthquake Mw 6.4 shook this region and was followed by series of major earthquakes (Mw>5.8) on 5, 9, and 19 August, which led to severe damage in the northern Lombok area. In this study, we attempt to reveal the possible cause of the sequences of the 2018 Lombok earthquakes based on aftershock monitoring data. Twenty stations were deployed to record earthquake waveform data from 4 August to 9 September 2018. In total, 3259 events were identified using 28,728 P- and 20,713 S-wave arrival times during the monitoring. The aftershock hypocenters were determined using a nonlinear approach and relocated using double-difference method. The moment magnitude (Mw) of each event was determined by fitting the displacement spectrum amplitude using a Brune-type model. The magnitudes of the aftershocks range from Mw 1.7 to 6.7. The seismicity pattern reveals three clusters located in the Flores oceanic crust, which fit well with the occurrences of the four events with Mw>6. We interpret these events as the main rupture area of the 2018 Lombok earthquake sequence. Furthermore, an aseismic zone in the vicinity of Rinjani extending toward the northwestern part of Lombok was observed. We propose that the crust in this area has elevated temperatures and is highly fractured thus inhibiting the generation of large earthquakes. The aseismic nature is therefore an artifact of the detection threshold of our network (Mw 4.6).
Earth and Space Science Open Archive This work has been accepted for publication in Journal of Geophysical Research - Solid Earth. Version of RecordESSOAr is a venue for early communication or feedback before peer review. Data may be preliminary. Learn more about preprints. preprintOpen AccessYou are viewing the latest version by default [v1]SASSY21: A 3-D seismic structural model of the lithosphere and underlying mantle beneath Southeast Asia from multi-scale adjoint waveform tomographyAuthorsDeborahWehneriDNienkeBlomiDNicholasRawlinsonDaryonoDaryonoChristianBoehmMeghan SamanthaMilleriDPepenSupendiSriWidiyantoroSee all authors Deborah WehneriDCorresponding Author• Submitting AuthorUniveristy of CambridgeiDhttps://orcid.org/0000-0001-9528-7304view email addressThe email was not providedcopy email addressNienke BlomiDUniversity of CambridgeiDhttps://orcid.org/0000-0001-8850-4358view email addressThe email was not providedcopy email addressNicholas RawlinsonUniversity of Cambridgeview email addressThe email was not providedcopy email addressDaryono DaryonoAgency for Meteorology, Climatology, and Geophysics (BMKG), Indonesiaview email addressThe email was not providedcopy email addressChristian BoehmDepartment of Earth Sciences, Institute of Geophysics, ETH Zürichview email addressThe email was not providedcopy email addressMeghan Samantha MilleriDAustralian National UniversityiDhttps://orcid.org/0000-0001-5494-2296view email addressThe email was not providedcopy email addressPepen SupendiAgency for Meteorology, Climatology, and Geophysics (BMKG)view email addressThe email was not providedcopy email addressSri WidiyantoroGlobal Geophysics Research Group, Faculty of Mining and Petroleum Engineering, Institut Teknologi Bandung, Indonesiaview email addressThe email was not providedcopy email address
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