臺灣重複地震區域特性分析與規模推估

Abstract

本研究利用寬頻地震網重新定義重複地震目錄，建置全臺灣規模2以上共329個重複地震序列，事件數達1853個，序列平均規模為2.52。臺灣之重複地震分別發生於六個構造分區:花東縱谷、中央山脈北段、苗栗、南投、中央山脈南段、台灣東南沿海地區，主要落在縱谷沿線和三義埔里地震帶。其中花東縱谷具有最多的序列量，佔全台灣序列的67 %，而花東縱谷北段和南投次之，佔10%。而於各區域進行平均滑移率的估計，大多介於3.5-4.0 cm/yr間。在六個分區中的重複地震，僅有花東縱谷區域的事件有明顯的線性分佈，對應到縱谷斷層南段池上斷層和中央山脈斷層北段的活動。另外，從區域平均滑移速率推估，發現當利用M≥3所決定的區域滑移速率，皆大於M>2的數值，然而他們表現的時間變異度高度相似，說明在重複地震目錄並不完整性的地區，較大規模重複地震所推求的時間演化趨勢，仍具有可信度。除此之外，本研究亦利用重複地震之路徑和場址效應具高相似度的特性，進行區域衰減式的推估（適用於縱谷地區），以用於未來重複地震即時偵測系統的規模決定。

Repeating earthquakes (RE) identified by nearly identical waveforms, location, and size represent repeated ruptures driven by aseismic slip in the surrounding. Given that their magnitude and recurrence interval are sensitive to the loading condition of fault, RE serves as a powerful tool to study the spatiotemporal distribution of aseismic slip behavior at depth. Here we build the M2+ repeating earthquakes catalog and investigate spatiotemporal distribution of aseismic slip behavior around Taiwan. During 2000-2011, about 1.3% of M2+ earthquakes (out of 134,731 events) in Taiwan were detected as repeating events. The 329 RE sequences composed of 1853 events are mainly located in six seismogenic regions: Longitudinal Valley, the north of Central Range, Miaoli area, Nantou area, south of Central Range area, and southeastern offshore area. The regional slip rates in most of the areas range from 3.5 to 4.2 cm/yr. In the six areas, only the events in the Longitudinal Valley region reveal linear trend, coinciding with the orientation of Longitudinal Valley and Central Range faults. Taking advantage of highly similar path effect of RE in a sequence, we obtained the empirical relation between magnitude and distance for individual RE. Various empirical relation obtained for different RE sequences indicates the strong variation in attenuation structure in Taiwan. These magnitude vs. distance relations provide a constraint for attenuation structure especially in where the RE are concentrated, eastern Taiwan.