- 學位論文
以區域波形震源逆推探討高加索至東土耳其之應力變化
Using Regional Waveform Source Inversion to Investigate Stress Variations in the Caucasus－Eastern Turkey Areas
摘要
阿拉伯板塊和歐亞板塊之間的碰撞在土耳其產生大型橫移斷層、將東安納托尼亞抬升為高原、並在高加索形成山脈。過去的研究裡高加索地區的震源機制都是利用遠震的波形資料針對中大規模的地震求解，小地震的研究較為缺乏，約束也較差。本研究使用新的測站陣列，以區域波形資料分析地震(規模3.5以上)的震源機制和深度，區域包括大高加索山、Javakheti高地以及土耳其東部。 研究結果顯示大高加索Racah地區的地震都為發生在上部以及中部地殼的北傾逆衝事件，其中2009/09/07序列的地震為1991 Mw7.0 Racha地震破裂帶的再次活動。土耳其東部以及亞美尼亞南部的地震是以上部地殼走向滑移事件為主，本研究在土耳其東部所得的三個走向滑移地震極有可能落在Sengaya-Gole 斷層上。在小地震頻繁的Javakheti高地有幾個規模4以下的地震，除了兩個於地震活躍區北邊的逆衝地震外，其他皆為走向滑移形式，與地表上的正斷層特徵不符。 應力分析顯示整個研究區域受到阿拉伯板塊推擠的影響，由南到北最大主應力(σ1)都維持在7-14°N的方向上。此外，大高加索地區的東西向中間主應力(σ2)也很可觀，足以產生東西或南北兩種走向的逆斷層。在土耳其東部則是垂直向的σ2與東西向的最小主應力(σ3)大小值相近，走向滑移與逆斷層可同時出現。小高加索Javakheti的應力分析結果也和土耳其相當類似，但呈現σ2–σ3環帶形貌（girdle）的應力不穩定狀況。
並列摘要
The continental collision between Arabia and Eurasia created large strike-slip faults in Turkey, uplift of East Anatolia and mountains in the Caucasus. In previous studies, focal mechanisms in the Caucasus are determined primarily for large earthquakes using global waveform data. Small earthquakes are less studied and poorly constrained due to limited stations in regional distances. In this study, we use regional waveforms of new array to constrain the focal mechanisms and depths of the earthquakes with M>3.5 in the major seismic zones in the Caucasus, Javakheti Highland (Lesser Caucasus) and eastern Turkey. Earthquakes in Racha of the Greater Caucasus are mainly thrust events with strikes in E-W direction confined in the upper to middle crust. Focal mechanisms and distribution of the 2009/09/07 earthquake sequence clearly show that they are the reactivation of 1991 Racha rupture fault zone. As for the eastern Turkey and Armenia, the earthquakes are upper crustal strike-slip events. Three of them may be directly associated with Sengaya-Gole fault in the eastern Turkey. Several focal mechanisms are in the Javakheti volcanic highland where swarms of small earthquakes are continuously occurring. Except for two small thrust events north of the swarm area, other earthquakes in this region are dominated by strike-slip faulting, which disagrees with normal structure inferred from the surface expression. With our and Global-CMT results, the formal stress inversion show that the maximum stress (σ1) is consistently in 7-14°N direction for the entire study region, which is apparently controlled by the northward movement of Arabia. In the Greater Caucasus, the W-E median stress (σ2) is considerable comparing to the N-S σ1, allowing both sub-EW and sub-NS striking thrust events to occur. As for the eastern Turkey, the vertical σ2 are more comparable to W-E minimum stress (σ3), such that the major strike-slip earthquakes coincide with a few thrusting events. The stress ratio in Javakheti region is similar to that of eastern Turkey but the σ2–σ3 girdle is much pronounced, suggesting that the permutation between the two stress axes is unstable.