Abstract

This work studies the characteristics of seismic coda waves attenuation in Eastern Anatolia. The short-period coda waves from about 400 earthquakes that occurred in Eastern Anatolia between 1989 and 2018 are analyzed. The three-component digital records of seismic events with M ≥ 3.5, recorded at epicentral distances of 10–600 kilometers, are used. S-wave attenuation was estimated from short-period coda envelopes (including those of Lg wave coda) at a frequency of ~1 Hz. The structural features of the S-wave attenuation field in the upper mantle of the Lake Van area are similar to those for other seismoactive zones. The attenuation field is represented by blocks, which have weak attenuation and are subisometric in plan view, and strong attenuation zones; in the case of blocks, attenuation decreases in the direction from the boundaries to the central of these blocks (Q-factor is up to 300–700). Among the zones of strong attenuation, which are usually linearly elongated, the most noticeable are the en echelon zone (north of 39° N), associated with the North Anatolian Fault; here, Q_S ~ 80–110 (up to Q_S ~ 60 in the north); and the Bitlis-Zagros fold and thrust belt (Q_S ~ 60–70). Sources of the strongest earthquakes with M > 6.0, including the 1976 Çaldıran–Muradiye and 2011 Van earthquakes, are confined to the boundaries of the blocks. The attenuation field structure corresponds to the velocity field structure: low-velocity anomalies correspond to low-Q zones. Vertically elongated volumes, with which intensive localized seismicity (earthquake swarms) is associated and along which deep fluids can migrate, are revealed. Seismic activation in such volumes precedes large seismic events (for example, the 2011 Van earthquake). It is assumed that such volumes can be interpreted as local seismogenic sources.

中文翻译：

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东安纳托利亚的S波衰减场和地震构造

摘要

这项工作研究了东部安纳托利亚地震尾波的衰减特征。分析了1989年至2018年在安纳托利亚东部发生的约400次地震的短时尾波。地震活动带的三分量数字记录中号≥3.5，记录在10-600公里的震中距，使用。从短周期的尾波包络（包括Lg波尾波的包络）以大约1 Hz的频率估计S波衰减。S的结构特点范湖地区上地幔的波衰减场与其他地震活动带相似。衰减场由块表示，这些块在平面图中具有弱衰减并且在等轴测图中具有很强的衰减区域。在块的情况下，衰减从这些块的边界到中心的方向减小（Q因子最大为300–700）。在通常呈线性延长的强衰减带中，最明显的是与北安纳托利亚断层有关的梯级带（北纬39°N）。这里，Q_小号〜80-110（高达Q_小号〜60在北方）; 以及Bitlis-Zagros褶皱和逆冲带（Q _S〜60–70）。M > 6.0的最强地震的来源，包括1976年的Çaldıran–Muradiye地震和2011年的Van地震，都局限于这些块体的边界。衰减场结构对应于速度场结构：低速异常对应于低Q区。揭示了垂直拉长的体积，与之相关的是强烈的局部地震活动（地震群），并且深部流体可以沿其移动。在这样的体积中，地震活动先于大型地震事件（例如2011年范地震）。假定这样的体积可以解释为局部震源。