FRACTAL GEOMETRY IN THE SAN-ANDREAS FAULT SYSTEM
FRACTAL GEOMETRY IN THE SAN-ANDREAS FAULT SYSTEM
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DOI：
10.1029/jb092ib01p00345
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发表时间：
1987-01-10
期刊：
影响因子：
--
通讯作者：
AKI, K
中科院分区：
文献类型：
--
作者：
OKUBO, PG;AKI, K
人们已经注意到，地震的空间分布和应变释放的方式在圣安德烈亚斯断层系统是与复杂的断层几何形状。由于断层在许多长度尺度上都是粗糙的，因此可以把它们看作是分形表面。直接估计的分维D的部分圣安德烈亚斯断层系统之间的北方加比兰山脉和索尔顿海，包括假定的1857年特洪堡大地震的范围，从测量的断层长度，类似于Mandelbrot所讨论的海岸线的长度。断层几何形状复杂的地区，D值较大。根据以1：750，000比例尺绘制的断层轨迹，该断层段的Dis为1.3，定义为围绕主断层轨迹的30 km宽的带。对于帕克菲尔德附近可能与1857年地震成核相关的部分，Dis为1.1;在相同的规模下，圣安德烈亚斯和圣贝纳迪诺附近的相关断层（1857年破裂停止处）的Dis为1.4，而1966年帕克菲尔德地震停止点附近的圣安德烈亚斯-圣胡安断层段的Dis为1.2。在更精细的地图比例尺（1：24，000和1：62，500）下，确定了10500 m和1 km的临界长度，这可能与圣安德烈亚斯断层偏移的范围有关。临界长度还表明断层几何形状不是自相似的。如果这种分形几何在地震周期中持续存在，就有可能使用复杂性的定量测量来解释沿着某一特定断层段发生的大地震和特征地震。
It has been noted that the spatial distribution of earthquakes and the mode of strain release in the San Andreas fault system is related to the complexity of fault geometry. Because of their rough appearance over many length scales, faults can be regarded as fractal surfaces. Direct estimates of fractal dimensionDof portions of the San Andreas fault system between the northern Gabilan Range and the Salton Sea, including the postulated extent of the great 1857 Fort Tejon earthquake, are obtained from measured fault lengths, analogous to the lengths of coastlines as discussed by Mandelbrot. Regions characterized by complicated fault geometry are associated with larger values ofD. Based on fault traces mapped at a scale of 1:750,000,Dis 1.3 for this reach of the fault defined as a 30‐km‐wide band about a main fault trace. For that part near Parkfield which could be associated with the nucleation of the 1857 earthquake,Dis 1.1; at this same scale,Dis 1.4 for the San Andreas and related faults near San Bernardino where the 1857 rupture stopped, compared to 1.2 for the San Andreas‐San Juan fault segments near the point of arrest of the 1966 Parkfield earthquake. At finer map scales (1:24,000 and 1:62,500) critical lengths of ∼ 500 m and 1 km are identified which might relate to the extent of off‐San Andreas fault offsets. The critical lengths also suggest that fault geometry is not self‐similar. If this fractal geometry persists through the seismic cycle, it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault.