Strain accumulation and release mechanism of the 1906 San Francisco Earthquake
Strain accumulation and release mechanism of the 1906 San Francisco Earthquake
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1906年旧金山地震应变积累与释放机制
DOI：
10.1029/jb080i035p04862
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发表时间：
1975
影响因子：
--
通讯作者：
W. Thatcher
中科院分区：
文献类型：
--
作者：
W. Thatcher
对大地测量数据的重新审查表明，在1906年大地震（M = 8.3）之前和之后都发生了显著的地壳变形。在1906年之前的150年里，横跨圣安德烈亚斯系统的100公里宽的区域的平均张量剪切应变率在0.4到0.9×10−6 yr−1之间，圣安德烈亚斯断层以东的应变率高于其以西的应变率。1906年，断层上的地震滑动突然释放了部分累积应变，但在地震发生后的30年里，断层附近的地震应变释放仍以1.2×10−6 yr−1的速率持续。从那时起，无论是在断层附近还是在其周围的广大区域，其速率都接近0.3×10−6 yr−1。我们认为，这些观测结果的机制是，在2080年的时间间隔内，圣安德烈亚斯板块边界450公里长的部分大部分区域逐渐发生了破坏。地震滑动平均接近4米，相对较浅，受数据限制深度不超过约10公里。由长周期面波振幅确定的地震矩为4.0×1027 dyn cm，与大地测量结果吻合较好。地震带下3-4 m至1.30km深度的持续地震滑动很好地解释了所有的震后资料。少量的震前观测结果与断层在更深处的快速滑动相一致。最后，在1906年之前观察到的高应变积累率对经常引用的圣安德烈亚斯断层上大地震的100年周期性提出了相当大的质疑，这似乎起源于H。F.里德的推论基于1906年前的变形。
Reexamination of geodetic data has shown that significant crustal deformation both preceded and followed the great 1906 earthquake (M = 8.3). In the ∼50 years prior to 1906, tensor shear strain rates averaged over an ∼100-km-wide region spanning the San Andreas system ranged from 0.4 to 0.9×10−6 yr−1, rates being higher east of the San Andreas fault than west of it. Part of this accumulated strain was released abruptly by seismic slip on the fault in 1906, but aseismic strain release continued at a rate of ∼1.2×10−6 yr−1 near the fault for about 30 years following the earthquake. Since that time the rate has been near 0.3×10−6 yr−1 both close to the fault and in a broad region surrounding it. The mechanism suggested to account for these observations is the progressive failure of most of a 450-km-long segment of the San Andreas plate boundary during an ∼80-year interval. The seismic slip, averaging near 4 m, is relatively shallow, being constrained by the data to depths no greater than about 10 km. The seismic moment determined from long-period surface wave amplitudes is 4.0×1027 dyn cm and agrees well with the geodetic estimates. Continued aseismic slip of 3–4 m below the seismic zone to depths of ∼30 km explains all of the postseismic data well. The small number of preearthquake observations are consistent with rapid slip on the fault at greater depths. Finally, the observation of a high rate of strain accumulation prior to 1906 casts considerable doubt on the often quoted 100-year periodicity of great earthquakes on the San Andreas fault, which appears to have originated with H. F. Reid's inferences based on the pre-1906 deformation.