Séminaire ISTerre

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Neotectonics of Indonesian Arc: Active thrust fault in the back-arc domain

mercredi 7 juin 2023 - 10h30

Sonny Aribowo - ISTerre / BRIN
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Indonesia is among the most seismically active countries in the world. Several regions along the Indonesian arc have experienced high-magnitude earthquakes. In addition to the subduction zone, the back-arc regions between the Nusa Tenggara Islands and Java, the most densely populated island in Indonesia, may result in destructive earthquakes. Also, the back-arc thrusts in Nusa Tenggara are experiencing earthquakes with magnitudes higher than 6.5 Mw. Yet, the mechanism and initiation of the back-arc thrust remain unclear. Upon entering Java Island, the E-W trending thrust bisects the northern part of the region. Yet, earthquakes and seismic risk in Java have parodically been understudied since there has been no major earthquake event in the last 200 years. In addition, the connection between the Flores Back-arc Thrust and the Java Back-arc Thrust remains elusive. I used a variety of data sources to understand the structure of the Wetar to Flores Back-arc Thrust, its relationship with the Java Back-arc Thrust, and the activity of the Java Back-arc Thrust that passes through several major cities on Java island. Those datasets include seismic reflection data, borehole data, onshore and offshore morphology, satellite gravity anomalies, and structural field observations. Seismic and gravity anomalies data reveal Early Miocene compression due to the Australian collision. During the Pleistocene, the compressional regime reactivated the thrusts in Nusa Tenggara Back-arc. In Java, the age of the thrust structure varies, making it more difficult to connect with the Flores-Wetar thrust. I find that the Java Back-arc Thrust system is partitioned in East Java and continuous to Central and West Java. In Central and West Java, faults, volcanoes, and sedimentary basins interact to modulate the propagation of faults and folds across and along strike. The Central Java Back-arc Thrust has been associated with a compressional tectonic regime since the Late Miocene and has propagated to the West Java Back-arc Thrust since the Pliocene. The activity of the fault then continues to present-day. Westward, in the Jakarta Basin, seismicity mostly occurs in the eastern part. A Pliocene structure initiation and tilting Holocene sediments, without marked fault ruptures confirm the immaturity of the structure in the western part of the Jakarta basin. Therefore, earthquake-induced blind thrusts are also expected, causing an important hazard, thereby exposing infrastructures and populations to a possibly high risk that needs to be evaluated.

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Equipe organisatrice : Organisation labo

Salle Dolomieu, Maison des Géosciences, 38400 Saint Martin d'Hères

Informations de visio :

https://univ-grenoble-alpes-fr.zoom.us/j/98030051610?pwd=aFBmM2c3VVIvc2tiNlV2R2M2WExZUT09

ID de réunion : 980 3005 1610
Code secret : 220865