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The Aftershock Analyses of the 27 February 2010 Chile M=8.8 Mega Earthquake
|Issue Date: ||2012-11-26T02:18:42Z
|Abstract: ||在1960年，智利南部曾經發生過規模9.5的巨大地震。後來也發生數起規模大於8的地震，這也暗示了該區域的應力並未釋放完全。2010年2月27日在智利中部馬烏萊(Maule)地區發生規模8.8大地震，震央位於智利第二大城市康賽普西翁(Concepcion)的北北東方向105公里(西經72.733度、南緯35.909度)，其地震深度為35公里深，是屬於納斯卡板塊碰撞且隱沒至南美板塊，逆衝形態的地震。而主震發生後造成地體構造的破裂，約500公里長，並且引發海嘯，造成多人傷亡和大量財產的損失。直到今天此區域的地震仍然頻繁的活動。主震發生後，同年7月我們也到達主震海域施放了18顆海底地震儀(Ocean Bottom Seismometer)，利用海底地震儀收集主震後餘震資料，記錄時間約23天。我們挑選P波和S波的到時，利用當地一維模型定位。結果顯示，在海溝左側有一序列的正斷層事件，可能表示海洋板塊隱沒至大陸板塊之下，其隱沒過程受到阻礙，而導致海洋板塊斷裂，並形成正斷層事件。而在海溝右側大部分的餘震發生在古老增積岩體的地層和隱沒帶中，而增積岩體前緣並未有很多地震，這表示此邊界可能是屬於較高角度的分歧斷層構造，也因此較為容易形成海嘯。本研究區域從1835年開始，應力一直持續被累積著，直到主震發生後累積的應力才被釋放，但由前人滑移模型研究中知道，該區域應力可能並未完全釋放，還是有發生大地震的潛在可能，其歷史記錄中，發生大地震周期可能介於80-100年之間。臺灣位處於隱沒帶交會處，而隱沒構造和智利地區也有相似之處，且又有明顯的分歧斷層分佈，如果活動起來，它的危險是不容忽視的。|
In 1960, the biggest earthquake (M=9.5), the human ever recorded event, occurred in south Chile. Subsequently several mega earthquakes (M >8) occurred, along the plate boundary. This imply that an incomplete release of tectonic energy. In February 27 2010, Chile mega earthquake (M=8.8) occurred at the Maule area in middle of Chile. The epicenter location is 105 km, NNE direction (35.9° S, 72.73° W) from Concepción, the second biggest city in Chile. The main shock, in which the focal depth is about 35 km, is a thrust – type subduction earthquake where the Nazca Plate subduct/collied into the South America Plate (the Chile subduction system). The main shock caused more than 500-km long rupture in the accretionary prism that produced a destructive tsunami. It killed many thousands of people and damaged more buildings. Even up to today, the aftershocks and volcanic activities still occur continuously in this region. In order to understand the processes, we have deployed 18 OBSs at 4 months after the main shock. We recorded a total of 23-day data (July 15 – August 8). In this study, we analyzed the P- and S-wave arrivals. The events were relocated by using one-dimensional local velocity model. Before the trench region the result is shown a sequence of normal faulting events. That sequence is possible because the oceanic plate is hardly to subduct beneath the continental plate, as the result of banding mechanism of oceanic plate. On the other hand, after the trench region most of events occur in the paleo-accretionary and fewer in frontal-accretionary prism, we suggest that this boundary is a high angle splay-fault structure and that maybe imply for possibility of generated tsunami. In this study area, the stress has accumulated since 1835. The amount of stress was released by the main shock occurred in 2010. From the slip model by previous studies, we compare our aftershock result to check the region of incomplete released by this mega earthquake event. Based on the historical studies, the period of the mega earthquake occur between ~80 and ~100 years. Taiwan and Chile region share similar tectonic features that is located along the subdcution zone. By numerous researches in Taiwan region, the splay-fault structures also being observed. If these structures were activated, it may possible generated a destructive tsunami.
|Appears in Collections:||[應用地球科學研究所] 演講及研討會|
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