碩士 / 國立臺灣海洋大學 / 應用地球科學研究所 / 100 / In the early morning of February 27, 2010, a mega-earthquake now known as the “Maule Earthquake” (M=8.8) took place in the Maule region in central Chile. In May 1960, Chile was hit by the largest earthquake ever recorded with a magnitude of 9.5. In general, the west coast of Chile is a convergent boundary between the Nazca and South American Plates, with the Nazca Plate subducting beneath the South American Plate in a NE direction. With a convergence rate of 6-7 cm per year, stress accumulates in the lower part of the oceanic plate to a certain extent resulting in huge destructive earthquakes. In 2010, our team deployed two Ocean Bottom Seismometer (OBS) arrays (the A and B arrays), with a total of 33 deployments to record the aftershocks along the rupture area. We collected data for a total of 46 days (July 15 to August 7 for the A array and August 14 to September 6 for the B array). The aim of our study was to analyze the distribution and characteristics of the aftershocks to get a better understanding of the tectonic activity after the main event, and conjecture on the seismogenic processes that occurred during the rupture. Using the Antelope software on the B array data we picked the P- and S-wave arrivals and located the events. To obtain more accurate earthquake epicenter locations we also applied the HypoDD software. We recognized a total of 1,972 events in 23 days of monitoring with many of them distributed along both sides of the trench. Immediately behind the trench axis, along the frontal accretionary prism, there is an aseismic zone, possibly due to the high content of water in the sedimentary strata. On the other hand, the paleo-accretionary prism on the landward side of the trench accumulated most of the earthquakes. These events focus at depths of 50-100 km in the subduction zone. This is called the seismogenic zone. The comparison of events before the main shock and the HypoDD results of this study show that most of the events cluster along the edge of the northern portion of the rupture zone. In addition, the events apparently increase in west of the trench and south of the main shock. We suggest that the subduction activity of the Nazca Plate released more energy in ruptures after the main shock. However, the stress is probably not totally released yet. The events cluster landward of the trench with a trend NNE-SSW at about 33.3°S, and change to the NW-SE direction at 34.3°S. Events extended to the area located at 34.5°S and 71.5°W. This is a new linear boundary in this area after the main shock. The boundary is probably located at the intersection between the Andean Cordillera and the central depression (Central Valley). There is a series of thrust and normal type faulting near Pichilemu. This was probably triggered by the main shock of the Maule rupture which caused a change on the subducted stress in this region. Further detailed study will be needed. The tectonic structure of Taiwan and Chile are similar. By studying the aftershock and crustal structure in Chile we hope to improve our understanding of the seismogenic zone, which may cause mega-earthquakes and tsunamis, in the Taiwan region and other subduction zones in the world.
| Identifer | oai:union.ndltd.org:TW/100NTOU5135011 |
| Date | January 2012 |
| Creators | Shih-Jie Wang, 王詩絜 |
| Contributors | Chao-Shing Lee, 李昭興 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 54 |
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