Seismic reflection profile
Example of a high-resolution seismic-reflection profile collected by the USGS offshore of Point Sal. The profile shows a cross-section of the earth's crust down to about 240 meters. The dashed red lines show the Hosgri Fault Zone, part of a strike-slip fault system that extends for about 400 kilometers along the California coast from Point Arguello to Bolinas. The thin magenta lines show layers in sedimentary deposits that are flat northeast of the fault zone and folded southwest of the zone. The yellow layer at the top of the profile consists of unconsolidated sediment, about 17 meters thick, deposited in approximately the last 20,000 years after the last sea-level lowstand. The blue line is the seafloor "multiple," an echo of the seafloor.