Deep-Focus Earthquake Analogs Recorded at High Pressure and Temperature in the Laboratory
Deep-Focus Earthquake Analogs Recorded at High Pressure and Temperature in the Laboratory
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DOI：
10.1126/science.1240206
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发表时间：
2013-09
期刊：
影响因子：
56.9
通讯作者：
A. Schubnel;F. Brunet;N. Hilairet;J. Gasc;Yanbin Wang;H. Green
中科院分区：
文献类型：
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作者：
A. Schubnel;F. Brunet;N. Hilairet;J. Gasc;Yanbin Wang;H. Green
描绘深层断层大多数破坏性大的地震起源于地壳，那里的摩擦和脆性断裂控制着能量的释放。强烈的地震也可能发生在地幔中，但它们的破裂动力学很难确定，因为更高的温度和压力起着更重要的作用。Ye等人（第1380页）分析了2013年鄂霍次克海8.3级地震（迄今为止记录的最大深层地震）及其相关余震产生的地震p波。地震沿着一条超过180公里长的断层破裂，结构的不均匀性导致俯冲板块大量释放应力。在一组补充的实验室变形实验中，Schubnel等人（第1377页）模拟了类似深地震的声发射事件的成核。这些事件是由橄榄石到尖晶石的瞬时相变引起的，这将发生在相同的深度，并导致在其他深层地震中观察到的大应力释放。地幔中矿物相变产生的裂缝产生的声发射类似于深部地震。亚稳态橄榄石相变可能引发冷俯冲岩石圈400 ~ 700公里深震源地震。为了探索这一机制的可行性，我们在高压（P = 2 ~ 5千兆帕斯卡）和窄温度范围（T = 1000 ~ 1250开尔文）下对锗橄榄石（Mg2GeO4）进行了实验室变形实验。我们发现，在橄榄石到尖晶石转变开始时，裂缝成核。这些裂缝是动态传播的（以不可忽略的剪切波速的一部分），因此产生了强烈的声发射。与深震源地震类似，这些声发射来自纯剪切源，服从古腾堡-里希特定律，而不遵循大森定律。显微结构观察证明，动态弱化可能涉及纳米晶尖晶石反应产物在地震应变速率下的超塑性。
Delineating Deep Faults Most large, damaging earthquakes initiate in Earth's crust where friction and brittle fracture control the release of energy. Strong earthquakes can occur in the mantle too, but their rupture dynamics are difficult to determine because higher temperatures and pressures play a more important role. Ye et al. (p. 1380) analyzed seismic P waves generated by the 2013 Mw 8.3 Sea of Okhotsk earthquake—the largest deep earthquake recorded to date—and its associated aftershocks. The earthquake ruptured along a fault over 180-kilometer-long and structural heterogeneity resulted in a massive release of stress from the subducting slab. In a set of complementary laboratory deformation experiments, Schubnel et al. (p. 1377) simulated the nucleation of acoustic emission events that resemble deep earthquakes. These events are caused by an instantaneous phase transition from olivine to spinel, which would occur at the same depth and result in large stress releases observed for other deep earthquakes. Fractures generated by mineral phase transitions in the mantle produce acoustic emissions that resemble deep earthquakes. Phase transformations of metastable olivine might trigger deep-focus earthquakes (400 to 700 kilometers) in cold subducting lithosphere. To explore the feasibility of this mechanism, we performed laboratory deformation experiments on germanium olivine (Mg2GeO4) under differential stress at high pressure (P = 2 to 5 gigapascals) and within a narrow temperature range (T = 1000 to 1250 kelvin). We found that fractures nucleate at the onset of the olivine-to-spinel transition. These fractures propagate dynamically (at a nonnegligible fraction of the shear wave velocity) so that intense acoustic emissions are generated. Similar to deep-focus earthquakes, these acoustic emissions arise from pure shear sources and obey the Gutenberg-Richter law without following Omori’s law. Microstructural observations prove that dynamic weakening likely involves superplasticity of the nanocrystalline spinel reaction product at seismic strain rates.