2010 Chile Earthquake Case Study

Introduction

In early 2010 central south Chile experienced a Mw = 8. 8 earthquake and large tsunami waves that devastated areas on the Chilean Pacific coast, nearby offshore islands, and areas near the epicenter. In addition to the tsunami, the earthquake had many other geological consequences including aftershocks, terrestrial and submarine land-sliding, elevation changes, and a gravity shift. The purpose of this paper is to discuss and analyze the earthquake, its consequences, the resulting damages, and mitigation.

The Main Event

Figure 3: Location of epicenter off the Pacific coast of Chile with the Chile Trench in white and slip contours in yellow (Melnick, et. al. , 2012) At 6:34 UTC on February 7th 2010 the 6th largest earthquake to ever be recorded, with Mw = 8. 8, occurred off the coast of central south Chile. Only weeks earlier, an earthquake occurred relatively nearby in Haiti, however the event in Chile was 500 times larger than the Haitian event (Chinn, 2011). The epicenter was determined to lie ~10 kilometers offshore Chile in the Pacific Ocean at ~35. 97 S, ~72. 87 W [Figure 3], with the hypocenter located ~22 kilometers down (Moscoso, et. al. , 2011). The dipping mega-thrust rupture plane extended bilaterally for 500 kilometers and considered to be a seismic gap along the 1835 rupture plane, most of the 1906 rupture plane, and the 1928/1985 inter- plate interface (Moscoso, et. al. , 2011). Various models suggest the seismic moment lies between 1. 8×1022 – 2. 6×1022 Newton-meters (Pollitz, et. al. , 2011). Broadband surface waves and back projection methods yield average rupture velocities ranging from 2. – 2. 5 kilometers per second (Lay, et. al. , 2010). The 130 second moment rate is characterized by an increase for 90 seconds and then a decrease for the final 40 seconds (Lay, et. al. , 2010). Consequences of the main event included aftershocks, tsunami waves, land sliding, ground changes, a gravity shift, and damages, which are further discussed below.

Increased by 40 bars (Ryder, et. al. , 2012). This increase in coulomb stress might have contributed to the 30,000 moderate to large aftershocks detected up to 2 months after the main event due to the fact that failure is considered to be promoted when coulomb stress exceeds a threshold of 0. 5 – 1. 5 bars (Ryder, et. al. , 2012). Most of the aftershocks were located ffshore near the plate interface, concentrated in low slip regions between 40 and 140 kilometers from the trench at depths ranging from 10 – 35 kilometers (Rietbrock, et. al. , 2012). Focal mechanisms indicate that thrust faulting dominates the area, with some areas of normal faulting (Rietbrock, et. al. , 2012).

Tsunami

The Pacific Ocean The main event caused significant seafloor uplift creating large tsunamis waves that radially propagated all over the Pacific Ocean away from the rupture over a 30 rc (Yamazaki and Cheung, 2011). Chilean eye witnesses report an initial recession before the main wave followed by various smaller waves and surges (Synolakis, 2011). Eye witnesses on the offshore Juan Fernandez Archipelago described the tsunami as a “rapid high tide” (Synolakis, 2011). The maximum tsunami characteristics include wave heights of over 8 meters, flow depths reaching up to 600 meters on offshore islands and 500 meters on the mainland, and inundation at elevations up to 10 meters above sea level (Synolakis, 2011).

Fishing boars washed up to 10 kilometers up river and a 3 meter diameter sandstone boulder found over 250 meters from shore at an elevation of 15 meters above sea level shows how strong the tsunami forces involved were (Synolakis, 2011). The most severe impacts were observed on the Chilean coastline adjacent to the epicenter from San Antonio – Tirua, and 670 km offshore on the Juan Fernandez Archipelago (Synolakis, 2011; Yamazaki and Cheung, 2011). The tsunami hit many areas close to the epicenter within 30 minutes of the main event, however due to bathymetry and coastline shape, tsunami directions, impacts, and arrival times vary. Synolakis, 2011; Yamazaki and Cheung, 2011). For example, Talcahuano Harbor located in The Bay of Concepcion 100 kilometers south of the epicenter experienced an impact from a resonated 129 minute period oscillating wave three hours after the main event (Yamazaki and Cheung, 2011). Resonance such as this occurred in various areas along the Chilean coastline, and was caused by standing and partial standing wave systems produced along the coast due to wave reflection between the continental shelf and the headlands, resulting in radiated tsunami energy to become trapped over the continental margin (Yamazaki and Cheung, 2011). . Land sliding The main event caused both terrestrial and submarine land sliding to occur in the area.

Around 30 slides were delineated, with a majority of them being submarine (Volker, et. al. , 2011). These submarine slides were confined to the walls of various submarine canyons, and were characterized as thin transitional slides retrograding into open slopes adjacent to the canyons (Volker, et. al. , 2011). To the north, large slip occurred mostly offshore with maximum displacement values of 20 meters west (Rietbrock, et. al. , 2012). To the south, slip magnitude was much less, and found to be confined beneath the coastline (Melnick, et. l. , 2012). Around 120 kilometers east of the trench lay a hinge which acts as a boundary between subsided areas in the east and uplifted areas in the west (Farias, 2010). Maximum uplift and subsidence values were determined to be 5. 7 meters and 2. 7 meters respectively (Synolakis, 2011). In some areas such as on the Arauco Peninsula where the largest coastal uplift occurred, platforms emerged [Figure 8], and in other areas small islands submerged below the sea (Fritz, et. al. , 2011).

Methods for obtaining subsidence and uplift used a combination of intertidal organism distributions, high tide marks, and GPS estimates (Melnick, et. al. , 2012). Gravity Shift After the main event a regional gravity decrease of 5 Gal east of the epicenter, and a less significant gravity increase west of the epicenter was detected by small changes in the trajectory of one of NASA’s GRACE [Gravity Recovery and Climate Expert] satellites (Han, et. al. , 2010). On land surface subsidence of the hanging wall and crustal dilation can account or the gravity decrease, while interior deformation of the polar opposites and surface uplift can account for the small offshore positive gravity anomaly (Han, et. al. , 2010). In addition the large amount of mass moved at a high magnitude velocity during the 2010 Maule Earthquake caused the Earth’s rotation to accelerate, taking a millisecond off of the day (Chinn, 2011). Casualties / Damages At least 521 casualties were reported along the Chilean continental coast and on the Juan Fernandez Archipelago, where a majority of public buildings and homes were destroyed, killing 18 people out of the 600 total population (Fritz, et. l. , 2011). 379 of the casualties can be attributed to the earthquake [mostly due to building collapse], and 124 can be attributed to the resulting tsunami wave (Fritz, et. al. , 2011). May of the casualties were people vacationing at camp grounds that got washed away on the Chilean coastline, where warning systems and geologic hazard knowledge were absent (Fritz, et. al. , 2011).

Widespread structural damage from earthquake shaking and tsunami induced deposition and erosion, including billions of dollars in material losses, was also reported (Fritz, et. l. , 2011). Further offshore on the island of Rapa Nui, the tsunami flooded homes, and moved some of the Moais, which are large statues that were carved out of stone by the ancient civilization that once thrived on the island, luckily no casualties were reported (Fritz, et. al. , 2011). Most of the aftershocks were concentrated deep enough such that ground movements were not large enough to propose a hazard to the surface, however some shallow large quakes might propose a hazard to areas in close proximity to the epicenter (Ryder, et. l. , 2012). 10. Mitigation Due to the fact that in 2010 Chile was considered either a third world or developing country where community based education is not available to the greater population, prior mitigation was at a minimum (Fritz, et. al. , 2011).. The Pacific Tsunami Warning Center issued a warning 5 minutes after the occurrence of the main event, however in many areas the tsunami reached the shore within 30 minutes of the main event, causing evacuations in areas close to the epicenter to be unsuccessful (Fritz, et. al. , 2011).

However many Chilean lives were saved due to education programs that were recently becoming available, evacuation drills, and ancestral earthquake and tsunami knowledge (Fritz, et. al. , 2011).

Conclusions and Future Recommendations

The 2010 Chile earthquake was a devastating geologic event that significantly altered the lives and geology within relatively close proximity to the epicenter. Geologists should continue to study these earthquakes inside and out to gain knowledge on earthquake forecasting, causes, effects, processes, and mitigation.

Mathematical models such as MOST can be used to model and recreate tsunamis by inputting information on bathymetry an d initial tsunami propagation conditions into non linear shallow water equations with spherical coordinates (Fritz, et. al. , 2011). Recent data previously interpreted to be seismic noise is now considered by seismic geologists to be small earthquakes called tremors characterized by slow slip occurring deep below the surface for weeks at a time with recurrence intervals of around 14 months (Chinn, 2011).

Monitoring these tremors allows stress build up to be quantified, which could lead to new ideas on prediction and forecasting of large earthquakes (Chinn, 2011). Chile should also design alarm systems like Japan has which automatically halt train lines, seal gas mains, and sounds alarms in residential areas, public areas, businesses, cities, and schools (Chinn, 2011). Tsunami Refuge centers [Figure 9] are beginning to be constructed in towns along the coastlines of Chile (Chinn, 2011).

These buildings are built to be over 10 meters high, and to fit over 1000 people(Chinn, 2011). The centers will stand on reinforced rounded concrete pillars that are built into a deep foundation such that they are resistant to erosion, allow water to flow underneath the building, and minimize debris impacts (Chinn, 2011). In addition, tension cables made of steel hold the building together and re-center it during and after earthquakes (Chinn, 2011).

Although too many lives were lost, and widespread damage resulted from the large 2010 Chile mega-thrust earthquake, studies have yielded information on future earthquakes to increase the safety of populations in areas at high risk for large earthquakes, in addition many lives were also saved thanks to current and ancient geologic hazard knowledge. Figure 9: Tsunami Refuge Center model (Chinn, 2011).

References

1. Chinn, P. (Director). (2011). Nova: Deadliest Earthquakes: Haiti and Chile [Documentary]. United States: PBS. Farias, M. , Vargas, G. , Tassara, A. , Carretier, S. , Baize, S. , Melnick, D. , & Bataille, K. (2010).
2. Land-level changes produced by the M (sub w) 8. 8 2010 Chilean earthquake. Science, 329(5994), 916 Fritz, H. M. , Petroff, C. M. , Catalan, P. A. , Cienfuegos, R. , Winckler, P. , Kalligeris, N. , & … Synolakis, C. E. (2011).
3. Field survey of the 27 February 2010 Chile tsunami. Pure And Applied Geophysics, 168(11), 1989-2010 Han, S. , Sauber, J. , & Luthcke, S. (2010).
4. Regional gravity decrease after the 2010 Maule (Chile) earthquake indicates large-scale mass redistribution. Geophysical Research Letters, 37(23) Lay, T. T. , Ammon, C. J. , Kanamori, H. H. , Koper, K. D. , Sufri, O. O. , & Hutko, A. R. (2010).
5. Teleseismic inversion for rupture process of the 27 February 2010 Chile (M (sub w) 8. 8) earthquake. Geophysical Research Letters, 37(13) Melnick, D. , Cisternas, M. , Moreno, M. , & Norambuena, R. (2012).
6. Estimating coseismic coastal uplift with an intertidal mussel; calibration for the 2010 Maule Chile earthquake (M (sub w) = 8. 8). Quaternary Science Reviews, 4229-42 Moreno, M. M. , Melnick, D. D. , Rosenau, M. M. , Baez, J. J. , Klotz, J. J. , Oncken, O. O. , & … Hase, H. H. (2012).
7. Toward understanding tectonic control on the M (sub w) 8. 8 2010 Maule Chile earthquake. Earth And Planetary Science Letters, 321-322152-165.
8. Moscoso, E. , Grevemeyer, I. , Contreras-Reyes, E. , Flueh, E. R. , Dzierma, Y. , Rabbel, W. , & Thorwart, M. (2011).
9. Revealing the deep structure and rupture plane of the 2010 Maule, Chile earthquake (Mw=8. 8) using wide angle seismic data. Earth And Planetary Science Letters, 307(1-2), 147-155 Pollitz, F. F. , Brooks, B. , Tong, X. , Bevis, M. G. , Foster, J. H. , Buergmann, R. , & … Blanco, M. (2011).
10. Coseismic slip distribution of the February 27, 2010 Mw 8. 8 Maule, Chile earthquake. Geophysical Research Letters, 38(9) Rietbrock, A. A. , Ryder, I. I. , Hayes, G. G. , Haberland, C. C. , Comte, D.
11. D. , Roecker, S. S. , & Lyon-Caen, H. H. (2012).
12. Aftershock seismicity of the 2010 Maule Mw=8. 8, Chile, earthquake; correlation between co-seismic slip models and aftershock distribution?. Geophysical Research Letters, 39(8) Ryder, I. , Rietbrock, A. , Kelson, K. , Buergmann, R. , Floyd, M. , Socquet, A. , & … Carrizo, D. (2012).
13. Large extensional aftershocks in the continental forearc triggered by the 2010 Maule earthquake, Chile. Geophysical Journal International, 188(3), 879-890. Tanimoto, T. , & Ji, C. (2010). Afterslip of the 2010 Chilean earthquake. Geophysical Research Letters, 37(22)
14. Vigny, C. C. , Socquet, A. A. , Peyrat, S. S. , Ruegg, J. C. , Metois, M. M. , Madariaga, R. R. , & … Kendrick, E. E. (2011).
15. The 2010 M (sub w) 8. 8 Maule megathrust earthquake of central Chile, monitored by GPS. Science, 332(6036), 1417-1421. Voelker, D. , Scholz, F. , & Geersen, J. (2011).
16. Analysis of submarine landsliding in the rupture area of the 27 February 2010 Maule earthquake, central Chile. Marine Geology, 288(1-4), 79-89. Yamazaki, Y. , & Cheung, K. (2011).
17. Shelf resonance and impact of near-field tsunami generated by the 2010 Chile earthquake. Geophysical Research Letters, 38(12)