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Evaluation of Different Earthquake Scaling Relations on the Generation Ocean Engineering 195 (2020) 106716 Contents lists available at ScienceDirect Ocean Engineering journal homepage: www.elsevier.com/locate/oceaneng Evaluation of different earthquake scaling relations on the generation of tsunamis and hazard assessment Zhisong Li, Chao An <, Hua Liu Key Laboratory of Hydrodynamics (Ministry of Education), School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University, Shanghai, China ARTICLEINFO ABSTRACT Keywords: Earthquake source details can hardly be determined accurately in a short time window after an earthquake. Tsunamis For rapid tsunami warning purposes, rupture parameters for a given earthquake magnitude are estimated Tsunami warning using empirical scaling relations. In this paper, we evaluate the effectiveness of several commonly-used scaling Scaling relations relations. It is found that, for the 2011 Tohoku earthquake, most scaling relations overestimate the rupture area and underestimate the average rupture slip, resulting in predictions of earlier wave arrivals and smaller wave amplitudes in comparison to recordings. The scaling relation that uses ``asperity size" instead of actual rupture area, presents a smaller rupture area and a larger average slip, leading to better tsunami predictions. While for the 2014 Iquique and 2015 Illapel tsunamis of relatively smaller earthquake magnitude, different scaling relations lead to comparable tsunami predictions. We further implement these scaling relations to study a potential earthquake in the Manila subduction zone. Results show that different scaling relations cause significant differences in the tsunami arrival time and wave amplitude at coastal cities, especially in the along-trench direction. Thus, to access the tsunami threat from mega-earthquakes and build early warning systems, it is necessary to select the appropriate scaling relations. 1. Introduction For the most recent tsunamis, in light of the deployment of seis- mometers, tsunami buoys and other types of sensors, various data of Most devastating tsunamis in history are caused by thrust earth- the earthquakes and tsunamis are recorded, and they can be utilized quakes in subduction zones, leading to severe damage to the coastal to infer the earthquake rupture process and source parameters. In par- community, such as the 1960 Mw 9:5 Chile earthquake (Cisternas et al., ticular, the Deep-ocean Assessment and Reporting of Tsunami (DART) 2005), the 1964 Mw 9:2 Alaska earthquake (Reimnitz and Marshall, project provides real-time tsunami measurements in the open ocean. 1965; Ichinose et al., 2007), the 2004 Mw 9:1 Sumatra earthquake (Lay Including such data in finite-fault inversions can promisingly recover et al., 2005; Titov et al., 2005), the 2011 Mw 9:1 Tohoku earth- the tsunami source and reproduce the tsunami recordings (Satake, quake (Simons et al., 2011; Fujii et al., 2011; Satake et al., 2013), 1987; Fujii et al., 2011; Satake et al., 2013; An et al., 2014; Heidarzadeh and two recent Chilean tsunamis in 2014 and 2015. The 2014 Iquique et al., 2016; An et al., 2017). On such basis, for early tsunami warn- earthquake occurred in the northern portion of the 1877 earthquake ing purposes, the Pacific Tsunami Warning Centre (PTWC) conducts seismic gap in northern Chile. Slip deficit of about 6 to 9 m may finite-fault inversions by making use of the DART data, and issues have accumulated since 1877. Post-event analysis of tsunami records accurate tsunami predictions (Wei et al., 2003, 2008). However, in shows that the shallow rupture near the trench is very small (Lay et al., areas where there lacks tsunami buoys, such as the South China Sea, 2014; An et al., 2014), which may otherwise cause significantly larger tsunami measurements are not available. As a result, most local tsunami tsunamis, as is the case for the Tohoku event. The 2015 Illapel tsunami was recorded by more than 20 gauges, but most of the gauges were warning systems rely on a different approach, which is called the located along the coastline. As a result, studies show large variance in tsunami scenario strategy. In such a strategy, for subduction zones with the east–west location of the fault rupture, and it is still not clearly potential tsunami genesis, uniform slip models are constructed before understood if there was significant shallow rupture near the trench an earthquake occurs, and the corresponding tsunamis are numerically (Tilmann et al., 2016; Li et al., 2016; Melgar et al., 2016; An et al., simulated. After an earthquake, tsunami warnings are issued based on 2017; An and Meng, 2017). the scenario with the most similar earthquake magnitude. To construct < Corresponding author. E-mail address: [email protected] (C. An). https://doi.org/10.1016/j.oceaneng.2019.106716 Received 18 June 2019; Received in revised form 4 October 2019; Accepted 10 November 2019 Available online 13 November 2019 0029-8018/© 2019 Elsevier Ltd. All rights reserved. Z. Li et al. Ocean Engineering 195 (2020) 106716 Fig. 1. Location of the tsunami gauges during the 2011 Tohoku event. The red and blue stars show the United States Geological Survey (USGS) epicenter and the centroid of global Centroid Moment Tensor (gCMT) solution (Ekström et al., 2012), respectively. The dark red diamonds indicate the DART buoy stations. The black triangles denote the coastal stations, which include GPS buoys, seabed wave gauges and coastal tide gauges (Kawai et al., 2013). The initial sea surface deformation in the blue rectangular is displayed in Fig.3a. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.) the uniform slip models, fault rupture parameters are obtained from et al.(2017) observed that the scaling behavior of the rupture area to a given earthquake magnitude according to empirical scaling relations moment is consistent for all cases except normal-faulting earthquakes. (Wells and Coppersmith, 1994; Blaser et al., 2010; Strasser et al., 2010; Empirical scaling relations are widely used to assess regional Murotani et al., 2008, 2013; Thingbaijam et al., 2017). tsunami hazards (Liu et al., 2009; Wu and Huang, 2009; Nguyen et al., Tsunami sources in reality involve temporal processes regarding 2014; Ren et al., 2017). In addition, local tsunami warning systems earthquake ruptures. For example, Ren et al.(2019) evaluated the also depend on such scaling relations. For instance, the South China impact of kinetic rupture on tsunami generation and propagation dur- Sea tsunami warning system operated by National Marine Environ- ing the 2004 Sumatra and 2011 Tohoku tsunamis. However, tsunami ment Forecasting Center (China) adopts the scaling relations given warning systems ignore such effects for the purpose of rapid warning. by Wells and Coppersmith(1994) and Ren et al.(2014). The Japan Scaling relations provide a quantitative relationship between rupture tsunami warning system operated by the Japan Meteorological Agency parameters (e.g., length, width, slip) and earthquake magnitude. They (JMA) (Kamigaichi, 2009) uses the following scaling relations: log L = are usually derived from the regression of large databases of historical 0:5Mw * 1:8 and L = 2W (L rupture length, W rupture width, Mw earthquakes. Due to the different database used and different type of earthquake magnitude). It should be noted that most of these scaling earthquakes, studies often obtain similar but slightly different scaling relations are derived from seismic data. There have been very few relations. For instance, Wells and Coppersmith(1994) compiled the studies that quantitatively evaluate their effectiveness in generating source parameters of 244 global earthquakes, classified them according tsunamis. In a most recent study, An et al.(2018) demonstrated that to their focal mechanism, and derived scaling relations for different slip heterogeneity can largely be ignored for tsunami warning purposes, types of earthquakes. Even though the moment magnitude of earth- and they also derived a scaling relation suitable for tsunami generation. quakes ranges Mw 5 ∼ 8 in their study, the scaling relations obtained In this study, we test the performance of four representative and for thrust earthquakes have been widely used to access the tsunami commonly-used scaling relations, given by Wells and Coppersmith hazards for magnitude 8 or larger earthquakes (Liu et al., 2009; Wu (1994) (hereafter referred to as Wells1994), Blaser et al.(2010) (here- and Huang, 2009; Nguyen et al., 2014). Blaser et al.(2010) extended after Blaser2010), Strasser et al.(2010) (hereafter Strasser2010) the earthquake catalog adopted by Wells and Coppersmith(1994) from and Murotani et al.(2013) (hereafter Murotani2013) respectively, by 244 to 283 earthquakes, by adding more subduction earthquakes of applying them to the 2011 Tohoku, 2014 Iquique and 2015 Illapel relatively higher moment magnitude (up to Mw 9:5). They derived a tsunamis. Stirling et al.(2013) compiled a worldwide set of scaling new set of scaling relations with special focus on the large subduction relations and evaluated their relevance to a range of tectonic regimes. zone earthquakes. Strasser et al.(2010) obtained similar scaling rela- They pointed out that the Wells1994 scaling relations are out of date in tions as Blaser et al.(2010)'s, by compiling 95 inter-plate earthquakes terms of data and hence should not be used if more modern scaling rela- in addition to Wells and Coppersmith(1994)'s earthquake catalogue, tions are available. However, since the Wells1994 scaling relations are with magnitude ranging from Mw 6:3 to Mw 9:4. Murotani et al. still widely adopted by tsunami modelers, it is included in the analysis (2008, 2013) collected the finite-fault slip models of plate-boundary of this study. The results of Strasser2010 are found to be very similar to earthquakes (Mw 6:7 ∼ 9:2) in the vicinity of Japan that occurred from that of Blaser2010, so it is excluded from the main text but provided in 1923 to 2011, and derived a scaling relation between the conventional the supplementary information and discussed in the discussion section.
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