Assessing tsunami hazard using heterogeneous slip models in the Mentawai Islands, Indonesia

Abstract

Tsunami hazard maps are generated for the coastline of the Mentawai Islands, West Sumatra, Indonesia, to support evacuation and disaster response planning. A random heterogeneous slip generator is used to forward model a suite of earthquake rupture scenarios on the Mentawai Segment of the Sunda Subduction Zone. Up to 1000 rupture models that fit constraints provided by coral and geodetic records of coseismic vertical deformation from major earthquakes in 1797, 1833 and 2007 are used to model inundation and to define a maximum inundation zone that envelopes all of these scenarios. Comparison with single-scenario hazard assessments developed by experts and agreed through scientific consensus shows that there is value in modelling a suite of scenarios in order to obtain a more robust and conservative estimate of potential inundated areas. Although both the model presented here and the single-scenario models are based on assumptions about the characteristics of future events using knowledge of past events, by sampling a range of plausible outcomes we gain a more robust estimate of which areas may be inundated during a tsunami within the bounds of the assumptions applied. Purpose of the hazard assessmentTo plan for tsunami evacuation at the community level, information is needed about which areas of the coast may be inundated during a tsunami event. Based on this information, communities can identify safe evacuation areas outside the inundation zone and the most efficient routes to reach these safe areas. For a government considering life safety as the first priority in managing a disaster, it is reasonable to plan evacuation areas based on a deterministic assessment of 'maximum credible' or 'worst-case' scenarios, to the extent that scientific knowledge, conservatism and the assumptions that we make can define these scenarios. In contrast, disaster management strategies targeting other losses (e.g. economic losses) accept a different level of risk and are designed for a certain level of risk tolerance based on probabilistic hazard assessments.

Response to Reviewer 2 (please see the supplement file)

“…The properties of the fault plane are consistent with the previous investigations. For instance, the depth is comparable with the source models of the past Mentawai-Sunda subduction earthquakes and the strike and dip angles are in line with the slab models of the Sunda subduction zone developed by the USGS (Newman et al, 2011;Satake et al, 2013;Philibosian et al, 2014;Yue et al, 2014;Hayes et al, 2009Hayes et al, , 2012. In addition, to stochastically generate the earthquake sources, the fault plane is divided into 10 km by 10 km sub-faults (see Fig.…”

From regional to local SPTHA: efficient computation of probabilistic tsunami inundation maps addressing near-field sources

“…Nevertheless, this is a point probably deserving further investigation, considering that Satake et al (2013) showed how inundation from the Tohoku 2011 tsunami was variably controlled by long-period offshore tsunami components on flat coastal plains and shorter-period peaks in steep coastal areas. Indeed, Gusman et al (2014) used two cycles of a tsunami for identifying similar waves. Conversely, since, as described in the next section, offshore wave comparison is not used anymore in the near-field, this issue will not apply for local sources.…”

Tsunami evacuation plans for future megathrust earthquakes in Padang, Indonesia, considering stochastic earthquake scenarios

“…The geometry is essential to outlining the earthquake source zone, whilst a so-called asperity zone determines the areas of concentrated slips within the fault plane. In general, modeling an earthquake rupture process in terms of earthquake source and asperity zones for the future tsunamigenic earthquakes in the Mentawai-Sunda region is complicated and has significant uncertainty Griffin et al, 2016). In this study, the future earthquake source area in the Mentawai segment is defined using the fault rupture areas of the historical subduction earthquakes in the Sunda subduction zone (see Muhammad et al, 2016, for details).…”

“…In addition, with the low-lying plain topographic features in Padang, the probability of large inundated areas and large inundation depths is also high (Borrero et al, 2006;Muhari et al, 2010Muhari et al, , 2011. In the past, two types of earthquake source scenarios have been mainly considered to develop tsunami risk mitigation plans in Padang: deterministic scenarios (Borrero et al, 2006;Schlurmann et al, 2010;Muhari et al, 2010Muhari et al, , 2011 and probabilistic scenarios (McCloskey et al, 2008;Griffin et al, 2016). These two methods have both advantages and disadvantages.…”

“…Therefore, extensive and detailed data regarding the regional seismological characteristics are essential to developing the probabilistic scenarios. In previous investigations, those regional earthquake characteristics have not been properly taken into account (McCloskey et al, 2008;Griffin et al, 2016). Recently, Muhammad et al (2016) have evaluated the tsunami potential in Padang by developing the stochastic tsunami simulation method, allowing us to generate numerous scenarios of stochastic tsunami hazard.…”