A tomographic study of the Long Valley caldera, California, using improved hypocenter locations and double difference tomography

Unrestricted Long Valley has been one of the most seismically active regions in California for the last 25 years. In addition to this seismicity, Long Valley is an active volcanic region. Ash from previous eruptions has fallen over an area including twelve states, extending as far east as Kansas. This seismic and volcanic activity has resulted in the region being densely populated with scientific instruments. These features make Long Valley an ideal location for a tomographic study. This study focuses on magma chamber location beneath the Long Valley Caldera. Using precisely relocated earthquake hypocenters from hypoDD (Waldhauser, 2001) I used a double-difference tomography program tomoDD (Zhang and Thurber, Aug. 2003) to determine the velocity structure beneath Long Valley Caldera. I then used the velocity data to determine the locations of the magma chamber and CO2 reservoir beneath the caldera from 1980 to mid-1997, 1997 to 1998, and 1999 to 2006.

过去25年间，隆谷（Unrestricted Long Valley）一直是加利福尼亚州地震活动最为活跃的区域之一。除地震活动外，该区域同时也是一处活跃的火山活动带。此前火山喷发产生的火山灰覆盖范围涵盖美国十二个州，向东最远延伸至堪萨斯州。受此类地震与火山活动影响，该区域布设了极为密集的科学观测仪器。上述特征使得隆谷成为层析成像研究的理想选址。本研究聚焦长谷破火山口（Long Valley Caldera）下方的岩浆房位置。本研究采用由hypoDD（Waldhauser, 2001）生成的精校正地震震源位置数据，并借助双差层析成像程序tomoDD（Zhang与Thurber，2003年8月），反演得到长谷破火山口下方的速度结构。随后，本研究利用上述速度结构数据，分别确定了1980年至1997年中期、1997年至1998年以及1999年至2006年三个时段内，破火山口下方的岩浆房与二氧化碳储库位置。