Investigation of Earthquake Sources and Fracture Origin of Crustal Seismic Coda Using Seismograms Recorded at Depth in the Cajon Pass Drillhole

这项研究将继续记录和分析放置在加利福尼亚州南部圣安德烈亚斯断层附近的Cajon Pass深钻孔中的深度为2.5公里的三轴10赫兹地震检波器。到目前为止，该仪器已经记录了数百次频率高达400赫兹的地震。大多数较大的地震是由2赫兹三轴地面地震仪同时记录的。结果表明，地面地震记录的高频波幅严重枯竭，井下地震记录具有较高的拐角频率和高频幂律振幅衰减。将在2.0公里和3.5公里深度安装额外的宽带地震传感器，以改进对自然地震活动的测量，并记录大量地震活动地壳中的微震标度。这项研究是国家减少地震灾害计划的一部分。

This research is to continue the recording and analysis of a triaxial set of 10 Hz geophones placed at a depth of 2.5 km in the Cajon Pass deep drill hole near the San Andreas fault in southern California. To date, the instrumentation has recorded several hundred earthquakes at frequencies up to 400 Hz. Most larger events were recorded simultaneously by a 2 Hz triaxial surface seismometer. Results suggest that surface seismograms are severely depleted in high frequency wave amplitudes and downhole seismograms have high corner frequencies and high frequency power law amplitude decays. Additional wide-band seismic sensors will be installed at 2.0 and 3.5 km depths in order to give an improved measure of natural seismicity and record microearthquake scaling in a volume of seismically active crust. This research is a component of the National Earthquake Hazard Reduction Program.