Hypocenter relocation of the aftershocks of the Mw 7.5 Palu earthquake (September 28, 2018) and swarm earthquakes of Mamasa, Sulawesi, Indonesia, using the BMKG network data

Abstract

On September 28, 2018, the Mw 7.5 earthquake occurred in Palu, Central Sulawesi, Indonesia. This earthquake produced strong tremors, landslides, liquefaction and a tsunami and caused thousands of fatalities and damaged houses and infrastructure. We have relocated 386 of the 554 Palu aftershocks by using the double-difference relocation method (hypoDD) from September 28 to November 22, 2018. The aftershock pattern is consistent with the crustal deformation in the area and generally shows that the events have a NW-SE trending of ~ 200 km in length and ~ 50 km in width. Most of the aftershocks are located to the east of the Palu-Koro Fault Line. Since November 2, 2018, there have been hundreds of swarm earthquakes in the area of Mamasa, West Sulawesi, which is about 230 km south of the city of Palu. Some of these earthquakes were felt, and houses were even damaged. We have relocated 535 of the 556 swarm earthquakes having a magnitude of M 2 to M 5.4. Our results show that the seismicity pattern has a dip that becomes shallower to the west (dipping at a ~ 45° angle) and extends from north to south for a length of ~ 50 km. We also conducted a focal mechanism analysis to estimate the type of fault slip for selected events of an M > 4.5 magnitude. Most of the solutions of the focal mechanism analysis show a normal fault type. This swarm earthquake probably corresponds to the activity of the fault in the local area.

Use of Local Seismic Network in Analysis of Volcano-Tectonic (VT) Events Preceding the 2017 Agung Volcano Eruption (Bali, Indonesia)

“…To assess the reliability of the event locations after the DD relocation, a statistical resampling approach, i.e., the "bootstrap" method, was implemented (Efron, 1982;Billings, 1994;Shearer, 1997;Supendi et al, 2019). The arrival times of both P and S waves of the 2,095 relocated events were substituted by samples drawn in the time residual distributions.…”

Characteristics of building fragility curves for seismic and non-seismic tsunamis: case studies of the 2018 Sunda Strait, 2018 Sulawesi–Palu, and 2004 Indian Ocean tsunamis

“…17b). Furthermore, in Palu, the earthquake intensity is estimated at VII to VIII on the Modified Mercalli Scale, but ground shaking was not the main cause of structural destruction (Kijewski-Correa and Robertson, 2018;Supendi et al, 2019). The likelihood of complete damage is also relatively high for low flow depth levels, so ground motion could have triggered liquefaction events and enhanced the building susceptibility to tsunami damage in the waterfront of Palu City.…”

“…This megathrust earthquake was the second largest ever recorded (Løvholt et al, 2006) and caused the deadliest tsunami in the world. Overall, a dozen Asian and African countries were devastated, with around 280 000 casualties (Asian Disaster Preparedness Center, 2007;Suppasri et al, 2011). Although earthquakes represent the main cause of tsunamis, non-seismic events such as landslides can also initiate tsunami waves (Grezio et al, 2017;Ward, 2001).…”

“…Tsunami fragility curves are functions expressing the damage probability of structures (or death ratio) based on the hydrodynamic characteristics of the tsunami inundation flow (Koshimura et al, 2009a, b). These functions have been widely developed after tsunami events such as the 2004 Indian Ocean tsunami (IOT; Koshimura et al, 2009a, b;Murao and Nakazato, 2010;Suppasri et al, 2011), the 2006 Java tsunami (Reese et al, 2007), the 2010 Chilean tsunami (Mas et al, 2012), or the 2011 great eastern Japan tsunami (Suppasri et al, 2012(Suppasri et al, , 2013. Several methods aim to develop building fragility curves based on (i) a statistical analysis of on-site observations during field surveys of damage and flow depth data (empirical methods) (Suppasri et al, 2015(Suppasri et al, , 2020, (ii) the interpretation of damage data from remote sensing coupled with tsunami inundation modelling (hybrid methods) (Koshimura et al, 2009a;Mas et al, 2020;Suppasri et al, 2011), or (iii) structural modelling and response simulations (analytical methods) (Attary et al, 2017;Macabuag et al, 2014).…”

“…From the field surveys conducted after the 2018 Sunda Strait (Syamsidik et al, 2019), 2018 Sulawesi-Palu (Paulik et al, 2019), and 2004 Indian Ocean (Khao Lak-Phuket, Thailand) (Foytong and Ruangrassamee, 2007;Ruangrassamee et al, 2006) events, we utilize three databases called DB_Sunda2018, DB_Palu2018, and DB_Thailand2004, respectively. In the literature, tsunami inundation modelling has been performed many times to better understand the tsunami hydrodynamics, especially for earthquake-generated tsunamis (Charvet et al, 2014;Gokon et al, 2011;Koshimura et al, 2009a;Macabuag et al, 2016;De Risi et al, 2017;Suppasri et al, 2011). Compared to the 2004 IOT, the 2018 Indonesian tsunamis are uncommon events remaining less understood.…”