Coastal uplift and tsunami effects associated to the 2010 Mw8.8 Maule earthquake in Central ChileReport as inadecuate

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On February 27, 2010 at 03:34:08 AM an Mw8.8 earthquake, with epicenter located off Cobquecura73.24°W; 36.29°S, severely hit Central Chile. The tsunami waves that followed this event affected the coastal regionsbetween the cities of Valparaíso and Valdivia, with minor effects as far as Coquimbo. The earthquake occurred along thesubduction of the Nazca oceanic plate beneath the South American plate. Coseismic coastal uplift was estimated throughobservations of bleached lithothamnioids crustose coralline algae, which were exposed after the mainshock between34.13°S and 38.34°S, suggesting the latitudinal distribution of the earthquake rupture. The measured coastal uplift valuesvaried between 240±20 cm at sites closer to the trench along the western coast of the Arauco peninsula and 15±10 cmat sites located farther east. A maximum value of 260±50 cm was observed at the western coast of Santa María Island,which is similar to the reported uplift associated with the 1835 earthquake at Concepción. Land subsidence values onthe order of 0.5 m to 1 m evidenced a change in polarity and position of the coseismic hinge at 110-120 km from thetrench. In four sites along the coast we observed a close match between coastal uplift values deduced from bleachedlithothamnioids algae and GPS measurements. According to field observations tsunami heights reached ca. 14 m in thecoastal area of the Maule Region immediately north of the epicenter, and diminished progressively northwards to 4-2m near Valparaíso. Along the coast of Cobquecura, tsunami height values were inferior to 2-4 m. More variable tsunamiheights of 6-8 m were measured at Dichato-Talcahuano and Tirúa-Puerto Saavedra, in the Biobío and Arauco regions,respectively, to the south of the epicenter. According to eyewitnesses, the tsunami reached the coast between 12 to 20and 30 to 45 minutes in areas located closer and faraway from the earthquake rupture zone, respectively. Destructivetsunami waves arrived also between 2.5 and 4.5 hours after the mainshock, especially along the coast of the Biobío andArauco regions. The tsunami effects were highly variable along the coast, as a result of geomorphological and bathymetriclocal conditions, besides potential complexities induced by the main shock.Nota general

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Author: Vargas Easton, Víctor; - Farías, Marcelo; - Carretier, Sébastien; - Tassara, Andrés; - Baize, Stéphane; - Melnick, Daniel; -



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