Frequency‐magnitude distribution of microearthquakes beneath the 9°50′N region of the East Pacific Rise, October 2003 through April 2004
Frequency‐magnitude distribution of microearthquakes beneath the 9°50′N region of the East Pacific Rise, October 2003 through April 2004
复制标题
2003年10月至2004年4月东太平洋海隆北纬9°50′区域下方微地震的频率-震级分布
DOI：
10.1029/2008gc002128
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发表时间：
2008
期刊：
影响因子：
3.7
通讯作者：
Maria Tolstoy
中科院分区：
文献类型：
--
作者：
D. Bohnenstiehl;F. Waldhauser;Maria Tolstoy
从7个月的海底地震仪部署（2003年10月至2004年4月）中重新定位的震源数据提供了一个机会来绘制沿东太平洋隆起9°49 - 52′n区域的微地震频率-震级分布（fmd）。这些分析包含了9000多次地震，代表了对任何洋中脊扩展中心的fmd的三维时空模式的首次调查。古腾堡-里希特模型很好地描述了这些数据，表明地震大小和频率之间存在幂律或分形关系。尺度指数（b值）表现出显著的空间变异性，在轴向最浅处超过2.0，在远离轴向波谷处降至1.0以下。这种空间格局与b值与环境应力条件之间的反比关系是一致的，在浅深度处观察到最低的应力水平，而在远离轴向区域的地方观察到相对较高的应力水平（或低孔隙压力）。在脊状系统熔融透镜上方的轴上观测到中间的b值；然而，在该区域内也存在显著的空间变异。这表明热液环流胞内的应力条件和/或结构非均质性可能在亚公里尺度上发生变化。虽然观测期的特征是地震活动性增加，并在2006年1月形成一次喷发，但b值的一阶空间格局是持续的，没有总体的时间趋势。作为这个b值分析的副产品，阵列的检测能力进行了经验评估。
Relocated hypocentral data from a 7‐month deployment (October 2003 to April 2004) of ocean bottom seismometers provide an opportunity to map microearthquake frequency‐magnitude distributions (FMDs) along the 9°49–52′N region on the East Pacific Rise. These analyses, which incorporate more than 9000 earthquakes, represent the first investigation of the 3‐D spatial and temporal patterns of FMDs along any mid‐ocean ridge spreading center. The data are described well by a Gutenberg‐Richter model, indicating a power law or fractal relationship between earthquake size and frequency. The scaling exponent, or b value, shows significant spatial variability, exceeding a value of 2.0 at the shallowest depths on axis and dropping below 1.0 away from the axial trough. This spatial pattern is consistent with an inverse relationship between b value and ambient stress conditions, with the lowest stress levels at shallow depths and relatively high stress levels (or low pore pressures) observed away from the axial zone. Intermediate b values are observed on‐axis above the ridge system's melt lens; however, within this region there also exists significant spatial variability. This indicates that stress conditions and/or structural heterogeneity may vary at subkilometer scales within the hydrothermal circulation cell. Although the observational period is characterized by increasing seismicity rates, building toward an eruptive episode in January 2006, the first‐order spatial pattern of b values is sustained, with no overall temporal trend. As a byproduct of this b value analysis, the detection capabilities of the array are assessed empirically.