Three-dimensional crustal structure of the Mendocino triple junction region from local earthquake travel times

The large-scale, three-dimensional geometry of the Mendocino Triple Junction at Cape Mendocino, California, was investigated by inverting nearly 19 000 P wave arrival times from over 1400 local earthquakes to estimate the three-dimensional velocity structure and hypocentral parameters. The evidence is interpreted as tectonic underplating of the Pacific oceanic crust beneath the coastal Franciscan Complex, similar to the situation seismically imaged in central coastal California. This geometry indicates that the westernmost portion of the slab window has been filled by tectonic underplating and crustal thickening, while deep-seated mantle upwelling is confined to an area centered about 75 km north of Clear Lake. -from Authors