Aftershock Sequence Analysis of the Mw 6.5 December 15, 2017 and the Mw 5.9 January 23, 2018 Java Earthquakes

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The west part of Java sits at the transition from oblique subduction along Sumatra to orthogonal convergence along central and eastern Java. This region has experienced several destructive earthquakes, the Mw 7.7 July 17, 2006 earthquake and tsunami off the coast of Pangandaran and the Mw 7 September 2, 2009 earthquake, located off the coast of Tasikmalaya. Both earthquakes were widely felt in Java. On December 15, 2017, the Mw 6.5 earthquake located off the coast near Pangandaran, and on January 23, 2018, the Mw 5.9 earthquake located offshore Lebak, between Pelabuhan Ratu and Ujung Kulon. The December event is located at 115 km, deeper than the January event (46 km). Ground shaking and damage occurred locally and in Jakarta on the northern coast of Java. Both earthquakes have NE-SW orientated strike-slip mechanisms. In this study, we use the HYPODD method to relocate both mainshocks and 10 months of seismicity (228 events) following the earthquakes. The relocation result improved the mainshock locations and depth distribution of seismic events. The December event is still deep (100.4 km) and its aftershocks locate up-dip at depths 50 – 80 km depths along the plate interface or the shallow part of the subducting slab. The January event is on the plate interface at 48.5 km depth and its aftershocks are in the overlying plate between 15 and 40 km depth. We observe a shallowing upward trend in the first 24 hours after the mainshock, suggesting that fluid migration might be involved. Seven months after this event, shallow (~10 km depth), NE-SW trending seismic activity is observed close to the coast.

Presenting Author: Anne M. M. Sirait

Authors