Microseismicity and stress in the vicinity of the Alpine Fault, central Southern Alps, New Zealand
Microseismicity and stress in the vicinity of the Alpine Fault, central Southern Alps, New Zealand
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新西兰南阿尔卑斯山中部阿尔卑斯断层附近的微震活动和应力
DOI：
10.1029/2011jb008460
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发表时间：
2012
影响因子：
--
通讯作者：
T. Stern
中科院分区：
文献类型：
--
作者：
C. Boese;John Townend;Euan Smith;T. Stern
我们研究了与阿尔卑斯山中部断层以及南阿尔卑斯山中部活动变形和隆起区相关的当今微震活动。使用 14 个月的数据，已经获得了约 1800 次震级在 -0.3 到 4.2 之间的地震的可靠震源位置。我们得出了一个震级标尺，其衰减系数与频率相关，γ(f) = γ0f，其中 γ0 = 1.89 ± 0.02 × 10-3 s/km，这使得能够对不同规模和频率内容的地震一致地计算震级。地震活动的最大深度随着距阿尔卑斯断层的距离而系统地变化，从断层附近的10±2公里到20公里内的8±2公里和更东南的15±2公里。这种分布与地壳电阻率的横向变化相关：地震震源集中在电阻率梯度较强的区域，并且仅限于电阻率>100 Ωm 的深度。更深处的岩石太热、液体太饱和或太弱而无法产生可检测到的地震。对 211 次地震 (ML > 0.44) 计算的震源机制解主要表现出走滑机制。通过震源机制反演得到最大水平压应力方向为115±10°。该方位角与南岛中部和北部其他地方的发现一致，表明尽管地壳结构和地形起伏存在明显变化，但地壳应力场是均匀的。我们的应力估计表明，阿尔卑斯断层（平均走向为 055°）在安德森意义上的定向很差，但断层表面痕迹的各个逆冲和走滑段具有接近最佳的方向。美国地球物理联盟版权所有 2012。
We investigate present-day microseismicity associated with the central Alpine Fault and the zone of active deformation and uplift in the central Southern Alps. Using 14 months of data, robust hypocenter locations have been obtained for ∼1800 earthquakes of magnitudes between -0.3 and 4.2. We derived a magnitude scale with a frequency-dependent attenuation factor, γ(f) = γ0f, where γ0 = 1.89 ± 0.02 × 10-3 s/km, that enables magnitudes to be calculated consistently for earthquakes of different sizes and frequency contents. The maximum depth of the seismicity varies systematically with distance from the Alpine Fault, from 10 ± 2 km near the fault to 8 ± 2 km within 20 km and 15 ± 2 km further southeast. This distribution correlates with lateral variations in crustal resistivity: earthquake hypocenters are concentrated in areas of strong resistivity gradients and restricted to depths of resistivities >100 Ωm. Rocks at greater depth are too hot, too fluid-saturated, or too weak to produce detectable earthquakes. Focal mechanism solutions computed for 211 earthquakes (ML > 0.44) exhibit predominantly strike-slip mechanisms. We obtain a maximum horizontal compressive stress direction of 115 ± 10° from focal mechanism inversion. This azimuth is consistent with findings from elsewhere in the central and northern South Island, and indicates a uniform crustal stress field despite pronounced variations in crustal structure and topographic relief. Our stress estimates suggest that the Alpine Fault (with a mean strike of 055°) is poorly oriented in an Andersonian sense but that individual thrust and strike-slip segments of the fault's surface trace have close to optimal orientations. Copyright 2012 by the American Geophysical Union.