Quaternary faults at San Diego Bay, California
Quaternary faults at San Diego Bay, California
复制标题
加利福尼亚州圣地亚哥湾的第四纪断层
DOI：
--
复制
发表时间：
1975
期刊：
影响因子：
--
通讯作者：
M. P. Kennedy
中科院分区：
文献类型：
--
作者：
G. Moore;M. P. Kennedy
海底地层的声反射剖面揭示了许多断层，这些断层切割了圣地亚哥湾内外的第四系沉积物。这些断层与之前绘制的陆上断层一起构成了玫瑰峡谷断裂带，该断裂带形成了圣安娜构造块的局部西边边界，东边与埃尔西诺断裂带接壤。圣地亚哥在历史时期感受到的、在过去41年中准确记录的小地震太罕见了，无法解释观测到的滑动速度。据推测，主要断层发生在中等地震期间，类似于1933年在加利福尼亚州长滩圣安娜地块西侧和1956年在下加利福尼亚州圣米格尔记录的前几次地震。这些先前发生的地震的已知震级表明，圣地亚哥的地震可能达到大约6.5级。拉霍亚角海岸的偏移量除以之前研究的6.5级地震的偏移量，表明这种事件大约每600年在那里发生一次。圣地亚哥海湾包括白垩纪、第三纪和第四纪地层(Kennedy和Moore，1971)。这些地层通常几乎是平坦的，但在与圣地亚哥湾西北方向的轴线平行的变形带内，被正断层和右旋断层局部褶皱和切割。这条变形的地带被称为玫瑰峡谷断裂带，暴露在加利福尼亚州圣地亚哥湾东南部和提华纳河三角洲旁边的下加利福尼亚州(Ziony，1973)，尤其是在海湾西北部的丘陵地带(Kennedy，1969)。在本次调查中，斯克里普斯海洋研究所的一艘船上使用声反射方法绘制了圣地亚哥湾下和银线滩外邻近海湾下的断层图。根据水平六分仪角度，导航定位的最大误差在海湾内为100米，在海湾外为300米。调查的声源是一个有60个电极的火花阵列，其底部穿透深度约为200米。每个电极5J的放电减少了混响，使地层分辨率达到约1m。致谢。我们感谢约翰·H·福斯特、尼尔·F·马歇尔和爱德华·E·韦尔戴，他们参与了这次巡航并对数据进行了分析。
Acoustic-reflection profiles of subbottom strata reveal numerous faults that cut Quaternary deposits within and directly outside of San Diego Bay. These faults, together with previously mapped onshore faults, constitute the Rose Canyon fault zone that forms the local west boundary of the Santa Ana tectonic block, which is bounded on the east by the Elsinore fault zone. The minor earthquakes that have been felt in San Diego during historic time and accurately recorded during the past 41 yr are too infrequent to explain the observed rate of slip. The principal faulting is inferred to take place during moderate earthquakes similar to previous ones recorded along the west side of the Santa Ana block in 1933 at Long Beach, Calif., and in 1956 at San Miguel, Baja California. The known magnitudes of these previous events suggest that earthquakes in San Diego could attain a magnitude of approximately 6.5. An offset of the coast at Point La Jolla, when divided by the offset associated with previously studied earthquakes of magnitude 6.5, suggests that such events occur there at an average of approximately once every 600 yr. The San Diego embayment contains Cretaceous, Tertiary, and Quaternary strata (Kennedy and Moore, 1971). These strata are generally nearly flat lying but are locally folded and cut by normal and right-lateral faults within a deformed belt that parallels the northwest-trending axis of San Diego Bay. This deformed belt, called the Rose Canyon fault zone, is exposed southeast of San Diego Bay in California and Baja California beside the delta of the Tijuana River (Ziony, 1973) and is especially well exposed in hilly terrain northwest of the bay (Kennedy, 1969). In the present investigation, acoustic-reflection methods were used aboard a Scripps Institution of Oceanography vessel to map the faults under San Diego Bay and under the adjacent bight outside Silver Strand barrier beach. Navigational fixes, by horizontal sextant angles, had a maximum error of 100 m within the bay and 300 m outside the bay. The sound source for the survey was a spark array with 60 electrodes that reached a subbottom penetration of about 200 m. Discharge of 5 J at each electrode reduced reverberation and allowed stratigraphic resolution of about 1 m. 1 California Division of Mines and Geology. Acknowledgments. We are indebted to John H. Foster, Neil F. Marshall, and Edward E. Welday, who participated in the cruise and in the analysis of the data.