High-Resolution Seismic Imaging for Managing Natural Resources and Hazards in the Southern California Coastal Zone

Abstract

The Coastal Zone is one of the most important regions of human occupation and development where coastal communities rely on the ocean for food, water, energy and commerce. Natural hazards along the California coast threaten human existence and productivity with storm surge and tsunami, sea level rise, active faulting, earthquakes, liquefaction and landslides, and sea water intrusion that corrupts inland groundwater basins. High-resolution seismic methods provide important subsurface data that cross the transition from sea to land where coastal hazards may affect infrastructure and human activities. In the shallow water along the coast, multichannel seismic reflection profiles are needed to attenuate the water bottom multiple and increase image depth for geologic interpretation. These images combined with coastal zone wells and boreholes provide data to decipher the geologic history and tectonic evolution necessary for understanding coastal hazards and resources. Examples of important coastal features identified and mapped along the southern California coast include filled Pleistocene river channels that provide alluvial basins with coarse materials suitable for subsurface seawater intake systems, yet also represent direct pathways for seawater intrusion across coastal fault barriers into nearshore groundwater basins. The major coastal fault systems which represent earthquake hazards are imaged and mapped in the subsurface where displaced and deformed coastal sedimentary sequences exist to provide timing of activity. Vertical deformation of these sequences may indicate prehistoric uplift or subsidence associated with tectonic activity and tsunami potential. Future deformation may disrupt major utilities and other infrastructure that cross the coastal zone from land to sea. Major active and ancient geologic structures identified include strike-slip faults associated with Pacific-North America transform plate boundary tectonics, oblique-reverse faults and folds associated with inverted Miocene rift basins subjected to Plio-Pleistocene transpression, and major extensional faults active along the coastal breakaway of the Transverse Ranges during the Neogene Inner Borderland rifting episode. High-resolution coastal zone geophysical imaging provides an important “Rosetta Stone” for understanding the natural resources, hazards and tectonic evolution of the southern California region.

AAPG Datapages/Search and Discovery Article #90339 ©2019 AAPG Pacific Section Convention 2019, Long Beach, California, April 1-3, 2019