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Mysterious Tsunami in the Caribbean Sea Following the 2010 Haiti Earthquake Possibly Generated by Dynamically Triggered Early Aftershocks

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Mysterious Tsunami in the Caribbean Sea Following the 2010 Haiti Earthquake Possibly Generated by Dynamically Triggered Early Aftershocks Earth and Planetary Science Letters 540 (2020) 116269 Contents lists available at ScienceDirect Earth and Planetary Science Letters www.elsevier.com/locate/epsl Mysterious tsunami in the Caribbean Sea following the 2010 Haiti earthquake possibly generated by dynamically triggered early aftershocks Uri ten Brink a, Yong Wei b,c, Wenyuan Fan d, Jose-Luis Granja-Bruña e, Nathan Miller a a USGS, Woods Hole, MA 02543, USA b JISAO, University of Washington, WA 98105, USA c NOAA-PMEL, Seattle, WA 98115, USA d Florida State University, Tallahassee, FL 32306, USA e Universidad Complutense de Madrid, Madrid, Spain a r t i c l e i n f o a b s t r a c t Article history: Dynamically triggered offshore aftershocks, caused by passing seismic waves from main shocks located Received 27 September 2019 on land, are currently not considered in tsunami warnings. The M7.0 2010 Haiti earthquake epicenter Received in revised form 3 April 2020 was located on land 27 km north of the Caribbean Sea and its focal mechanism was oblique strike- Accepted 5 April 2020 slip. Nevertheless, a tsunami recorded on a Caribbean Deep-Ocean Assessment and Reporting of Tsunami Available online xxxx (DART) buoy and a tide gauge produced runup heights of 1–3 m along Haiti southeast coast. Earthquake Editor: M. Ishii finite-fault model inversions of the DART waveform suggest that a reverse fault doublet with magnitudes Keywords: of M6.8 and M6.5 located 85 km southwest of the epicenter may have excited the tsunami. This doublet dynamically-triggered aftershocks collocates with dynamically triggered aftershocks, derived from back-projection analysis, that occurred instantaneous aftershocks 20-60 s after the main shock of the Haiti earthquake. The aftershocks are within a region of maximum tsunami warning protocol dynamic strain predicted by the main shock, on a possibly tectonically active submarine ridge southwest DART buoy of Haiti’s Southern Peninsula. The agreement between the tsunami finite-fault source models and the tsunami from land-based earthquake seismic and tectonic evidence suggests that earthquakes on land, even strike-slip faults, can generate tsunami from strike-slip earthquake tsunamis by dynamically triggering offshore aftershocks. Published by Elsevier B.V. 1. Introduction along offshore faults north of the peninsula (Symithe et al., 2013). In contrast, there is a paucity of aftershocks along the south shore The M7.0 2010 Haiti earthquake along the Enriquillo Fault west of the peninsula (Douilly et al., 2013). of Port-Au-Prince, Haiti, ruptured a complex fault network includ- Fritz et al. (2013)modeled the tsunami south of the island ing both strike-slip and reverse faults (Hayes et al., 2010). The rup- with mainshock source parameters close to the parameters pro- tured fault network was less than 60 km long, spanning from the vided by the global CMT solution (http://www.globalcmt .org/) but northern side of Haiti’s Southern Peninsula on land to the north with two crucial differences. The Fritz et al. (2013)model re- of the peninsula offshore (Fig. 1). The offshore rupture produced quired a uniform 5.8 m slip model, yielding a total moment a minor tsunami that impacted the north shore of the peninsula magnitude of 7.47, whereas the moment magnitude of the earth- (Hornbach et al., 2010; Fritz et al., 2013). Intriguingly, a much quake was 7.0 (https://earthquake .usgs .gov /earthquakes /eventpage / more prominent tsunami was reported along the south shore of usp000h60h/). In addition, the modeled fault dipped southward, the peninsula, in the Caribbean Sea, with 3 m runup in Jacmel whereas both the CMT solution and the interferometric synthetic- and 1 to 2 m runups as far east as Pedernales on the Domini- aperture radar (InSAR) inversion (Hayes et al., 2010) suggested a can Republic border (Fritz et al., 2013). The static Coulomb stress north-dipping fault. Consequently, the Fritz et al. (2013)source change from the 2010 Haiti earthquake mainshock can explain the model would predict a broad co-seismic uplift reaching the south majority of observed aftershocks, which are located west and east coast, which was not observed in the InSAR data (Hayes et al., of the mainshock along the northern part of the peninsula and 2010; Symithe et al., 2013). We propose that near-instantaneous dynamically-triggered af- tershocks located in the Caribbean Sea ∼85 km southwest of the E-mail address: [email protected] (U. ten Brink). mainshock epicenter generated the tsunami south of the island. https://doi.org/10.1016/j.epsl.2020.116269 0012-821X/Published by Elsevier B.V. 2 U. ten Brink et al. / Earth and Planetary Science Letters 540 (2020) 116269 ◦ ◦ Fig. 1. Finite-fault model with strike of 132 and dip of 84 . Models with other strikes and dips are shown in Fig. 3 and in the Appendix. (a) Grid of rectangular elements - Finite-fault model configuration. Line thickness denotes modeled slip amplitude. See Table S1 for coordinates and slip of the finite faults. Downdip width of all sub-faults is 20 km and their top depth is 1 km. Colors denote vertical seafloor deformation from the tsunami source model calculated using Okada’s (1985)analytical functions for an elastic half space. Yellow contours – Peak back-projected energy contours of the main shock and the three early aftershocks with values increasing inward from 60% to 90% (Fan and Shearer, 2016). Background – Shaded topography and bathymetry with selected elevations marked by white triangles. Topography is from SRTM 90 m grid. Shaded relief bathymetry is multibeam bathymetry compilation from various surveys gridded at 250 m and GEBCO grid. Red star – Epicenter of the 2010 Haiti earthquake. Purple lines – Seismic profiles shown in Fig. 4. Black dots – Campaign GPS sites. White rectangle – Location of map in (c). Inset: Locations of DART buoy and the Santo Domingo tide gauge station. (b) modeled and observed tsunami wave amplitudes at the DART buoy (top) and the Santo Domingo Tide Gauge (bottom). The inversion aims to fit the first observed waves on the DART buoy. (c) Calculated wave amplitude in the vicinity of Jacmel Bay (top) and calculated (black) and observed (orange) runup along the shoreline plotted by shoreline longitude. (For interpretation of the colors in the figure(s), the reader is referred to the web version of this article.) We conducted a systematic search for the tsunami source(s) by fit- after the main shock rupture (D’Amico et al., 2010; Nissen et al., ting the sea-surface elevation waveform recorded on Deep-Ocean 2016; Wang et al., 2016; Fan and Shearer, 2016). (The term after- Assessment and Reporting of Tsunami (DART) buoy 42407 located shock is used here to denote events that follow the largest shock in the Caribbean basin south of Santo Domingo (Fig. 1), as well of the earthquake sequence within the adjacent region). These af- as the tsunami arrival time at the Santo Domingo tide gauge, and tershocks are triggered by transient passing seismic waves, such as the observed tsunami runup at Jacmel. Our best-fit sources are col- seismic surface waves (Gomberg et al., 2001). They differ from stat- located with a shallow submarine ridge complex, which was pre- ically triggered aftershocks, which are caused by the permanently viously proposed to be tectonically active (Bien-Aime Momplaisir, altered Coulomb stress state in the crust and which are often lo- 1986), and with independently located, near-instantaneous dynam- cated within one fault length of the mainshock fault (e.g., Harris, ically triggered aftershocks of the earthquake (Fan and Shearer, 1998). Dynamically triggered aftershocks can be almost as large as 2016). the main shock, such as with the M 7.0-7.1 1997 Harnai, Pakistan Near-instantaneous dynamically triggered aftershocks have been earthquake with a M 6.8 aftershock 19 s later on a separate re- identified in the near to intermediate field during or immediately verse fault 50 km away (Nissen et al., 2016). In contrast, statically U. ten Brink et al. / Earth and Planetary Science Letters 540 (2020) 116269 3 geneous with 1 m slip on each sub-fault. The inversion procedure assimilates the observed tsunami waveforms and gradually adjusts the slip at each sub-fault, rendering most of them zero slip. Ta- ble S1 lists the geographical coordinates and slip amount for each sub-fault with slip > 0 for each model. We used the MOST (Method of Splitting Tsunami) model (Titov and Synolakis, 1995, 1998) for tsunami simulations. MOST solves the nonlinear depth-integrated shallow water equations, which are derived from the Navier-Stokes equations with the assump- tions that 1) the tsunami waves propagate in an incompressible and irrotational medium; 2) tsunami propagation is primarily dominated by the geometry of the ocean floor; and 3) tsunami waves have much greater horizontal length scale than vertical length scale. MOST is capable of simulating tsunami generation, transoceanic propagation, and inundation and is the standard model used at the NOAA Center for Tsunami Research. The MOST model has been numerically verified against laboratory experi- mental results and benchmarks (Synolakis et al., 2008) and fur- ther validated with modern tsunamis simulated both after the Fig. 2. Comparison of modeled tsunami wave amplitudes at the DART buoy (top) and the Santo Domingo Tide Gauge (bottom) for models with different rakes. All fact and in real time (Tang et al., 2016; Wei et al., 2013; Tang ◦ ◦ models have strike of 132 and dip of 84 similar to Fig. 1. et al., 2012; Wei et al., 2008). MOST uses the Manning’s coef- ficient to account for the frictional resistance that the tsunami triggered aftershocks are often 1 to 1.2 magnitude units smaller flow experiences when passing over the earth surface.
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