Cooling magma model for deep volcanic long-period earthquakes
Cooling magma model for deep volcanic long-period earthquakes
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DOI：
10.1002/2014jb011180
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发表时间：
2014-11-01
影响因子：
3.9
通讯作者：
Tsai, Victor C.
中科院分区：
文献类型：
--
作者：
Aso, Naofumi;Tsai, Victor C.
深源长周期事件（DLP事件）或深源低频地震（深源LFEs）是辐射低频地震波的深源地震。虽然板块边界上的构造深部LFEs被认为是滑动事件，但对火山下莫霍面（壳幔边界）周围火山DLP事件的物理机制的研究数量有限。一个合理的机制能够产生他们的初始裂缝是热应力的影响。由于上升的岩浆底辟倾向于停滞在莫霍面附近，那里的密度垂直梯度高，我们认为，冷却的岩浆可能在火山DLP事件的发生中发挥了重要作用。假设半宽为41米的板状岩浆或半径为74米的圆柱状岩浆内的初始热扰动为400 ℃，侵入岩浆内的热应变速率高于构造应变速率（约为10（-14）s（-1）），产生的总应变为2 × 10（-4）。由热应变产生的剪切脆性断裂可以产生所观察到的补偿线性矢量偶极机制，并且还可能解释来自激发共振的谐波地震波形。在我们的模型中，我们预测了星团的特定形状与震源机制的方向之间的相关性，这部分得到了阿索和Ide（2014）的观测结果的支持。为了评估我们的冷却岩浆模型作为火山DLP事件的原因的一般性，关于重新定位和焦点机制的额外工作是必不可少的，并且对于理解引起火山DLP事件的物理过程是重要的。
Deep long-period events (DLP events) or deep low-frequency earthquakes (deep LFEs) are deep earthquakes that radiate low-frequency seismic waves. While tectonic deep LFEs on plate boundaries are thought to be slip events, there have only been a limited number of studies on the physical mechanism of volcanic DLP events around the Moho (crust-mantle boundary) beneath volcanoes. One reasonable mechanism capable of producing their initial fractures is the effect of thermal stresses. Since ascending magma diapirs tend to stagnate near the Moho, where the vertical gradient of density is high, we suggest that cooling magma may play an important role in volcanic DLP event occurrence. Assuming an initial thermal perturbation of 400 degrees C within a tabular magma of half width 41m or a cylindrical magma of 74m radius, thermal strain rates within the intruded magma are higher than tectonic strain rates of similar to 10(-14)s(-1) and produce a total strain of 2x10(-4). Shear brittle fractures generated by the thermal strains can produce a compensated linear vector dipole mechanism as observed and potentially also explain the harmonic seismic waveforms from an excited resonance. In our model, we predict correlation between the particular shape of the cluster and the orientation of focal mechanisms, which is partly supported by observations of Aso and Ide (2014). To assess the generality of our cooling magma model as a cause for volcanic DLP events, additional work on relocations and focal mechanisms is essential and would be important to understanding the physical processes causing volcanic DLP events.