On February 27, 2010 a catastrophic magnitude 9 earthquake and accompanying tsunami struck the coast of central Chile. The effects of this event were particularly devastating in the area surrounding Concepción, the second largest city in Chile. This project will precisely document the geomorphic and tectonic signatures of this earthquake and tsunami at several previously described study sites in the Concepción region. In 2009 and early 2010 the author and Chilean collaborators described and surveyed tsunami deposits and uplifted coastal marine platforms at 10 sites between 36.5°S to 38.5°S. Lat. The objectives of this project are twofold: 1) Investigate deposits and impacts of the 2010 tsunami at existing study sites containing geological and historical evidence of previous tsunamis in the Concepción area; and 2) Assess co-seismic and post-seismic land-level changes at existing study sites that underwent significant uplift in previous earthquakes. Field work will be conducted in two separate field excursions between May, 2010 and January, 2011. Field investigations will include mapping and surveying the erosional and depositional effects of the 2010 tsunami at the previously documented sites to compare the deposits from the 2010 tsunami with those from previous events; calibrate the sedimentary deposits with the observational data; assess the preservation potential of tsunami deposits in this environment; and use the 2010 deposits to guide the search for additional repositories where stratigraphic records of multiple paleotsunami deposits are likely to be preserved. At the locations of land-level changes the field objectives will be to resurvey heights of marine platforms that were uplifted during previous earthquakes and surveyed by our team in January, 2010; determine the amount of additional uplift in the 2010 earthquake; establish a baseline elevation for subsequent monitoring of post-seismic land-level changes; and compare locations and amount of uplift in the 2010 earthquake with that measured after the 1835 earthquake.
This research has the potential to advance knowledge of the impacts, recurrence, and geological signatures of catastrophic events on the scale of the 2010 Chilean earthquake, which could lead to better preparation, education and decreased loss of life in similar coastal areas. The project will occasion U.S.-Chile collaboration that fosters mutual exchanges of knowledge and expertise. An accurate measurement of the effects of the recent tsunami and coastal uplift from the earthquake, together with the prior measurements, will enable a complete documentation of recurrence intervals of these events and the areas that are most affected. These data will be of great value in the rebuilding process for the communities devastated by the most recent event, and the investigation will have a sustainable presence where it will be most needed and useful.
On February 27, 2010, an enormous earthquake of magnitude 8.8 struck the coast of Chile. Only five earthquakes in the world since 1900 have been larger. The uplift of the seafloor during the earthquake triggered a tsunami that swept the coast. More than 525 people were killed. Insured losses were between four and seven billion US dollars, and estimates of total economic losses ranged from US$15-30 billion. We documented and compared observations of the geologic effects of the 2010 Chilean earthquake and tsunami with those of similar, earlier events over the last several hundred years in the same region. As a consequence we have significantly more confidence in our interpretation of the geologic evidence for prehistoric earthquakes and tsunamis, thus improving our knowledge of the chronology and distribution of these types of catastrophic events in Chile. The insights gained from this work will benefit similar studies in comparable geologic settings in the Pacific Northwest and Alaska, and will help us determine how to better prepare for future earthquakes and tsunamis. On February 20, 1835, a similar earthquake and tsunami struck the same region of central Chile that was hit in 2010. Fortunately for science, both the damage and geologic effects of the earthquake and tsunami in 1835 were documented in considerable detail by Charles Darwin and his colleague, Captain Robert FitzRoy, of the HMS Beagle. In the two years prior to the 2010 earthquake we had undertaken geologic studies of the 1835 and previous earthquakes and tsunamis along this region of the coast. We explored coastal marshes in search of unusual deposits of sand that would indicate a powerful wave sweeping landward. Following the 2010 earthquake, we revisited the regions of coast that we had studied prior to the earthquake and tsunami. We observed the actual geologic effects of the 2010 earthquake and tsunami and compared them with those that we had inferred for the 1835 and earlier tsunamis. For example, near the town of Tirua we found fresh deposits of sand from the 2010 tsunami over a mile inland. These deposits buried 3-4 similar layers of sand that were almost certainly caused by tsunamis that occurred within the last several hundred years. About six weeks after the 1835 earthquake FitzRoy and the Beagle visited a small island, Isla Santa María, about 15 miles off the coast, also in the region that had been affected by the earthquake. FitzRoy was amazed to discover that the island had been uplifted 8 to 10 feet during the earthquake. When we visited the island before the 2010 earthquake, we became convinced that the island had subsided about half of the amount of the 1835 uplift. The evidence for this included interviews with local residents describing the loss of low-lying land over several decades and our own repetition of the Beagle’s survey of the water depth in a shallow bay adjacent to the island. Following the 2010 earthquake, we observed a repetition of the phenomena observed by FitzRoy in 1835, intra-tidal and sub-tidal sea life killed by uplift above the reach of the tides. Studies of the sea life and surveys of the land height and water depth by ourselves and Chilean colleagues in 2010 and 2011 indicated that the island was again uplifted several feet during the 2010 earthquake. The pattern of uplift of the island during earthquakes, and subsidence in the period between large earthquakes is consistent with predictions based on the geologic theory of elastic strain accumulation and rebound, first developed by H.F. Reid following the 1906 San Francisco earthquake. Our results provide some of the first evidence over the entire interval between great earthquakes in support of this theory.
