Geology topics

Research about San Diego Bay

Source-linked reports with geographic coverage including San Diego Bay.

3 recordsLinked to original sources

USGS2021

Recency of faulting and subsurface architecture of the San Diego Bay pull-apart basin, California, USA

In southern California, plate boundary motion between the North American and Pacific plates is distributed across several sub-parallel fault systems. The offshore faults of the California Continental Borderland (CCB) are thought to accommodate ~10-15% of the total plate boundary motion, but the exact distribution of slip and the mechanics of slip partitioning remain uncertain. The Newport-Inglewood-Rose Canyon fault is the easternmost fault within the CCB whose southern segment splays out into a complex network of faults beneath San Diego Bay. A pull-apart basin model between the Rose Canyon and the offshore Descanso fault has been used to explain prominent fault orientations and subsidence beneath San Diego Bay; however this model does not account for faults in the southern portion of the bay or faulting east of the bay. To investigate the characteristics of faulting and stratigraphic architecture beneath San Diego Bay, we combined a suite of reprocessed legacy airgun multi-channel seismic profiles and high-resolution Chirp data, with age and lithology controls from geotechnical boreholes and shallow sub-surface vibracores. This combined dataset is used to create gridded horizon surfaces, fault maps, and perform a kinematic fault analysis. The structure beneath San Diego Bay is dominated by down-to-the-east motion on normal faults that can be separated into two distinct groups. The strikes of these two fault groups can be explained with a double pull-apart basin model for San Diego Bay. In our conceptual model, the western portion of San Diego Bay is controlled by a right-step between the Rose Canyon and Descanso faults, which matches both observations and predictions from laboratory models. The eastern portion of San Diego Bay appears to be controlled by an inferred step-over between the Rose Canyon and San Miguel-Vallecitos faults and displays distinct fault strike orientations, which kinematic analysis indicates should have a significant component of strike-slip partitioning that is not detectable in the seismic data. The potential of a Rose Canyon-San Miguel-Vallecitos fault connection would effectively cut the stepover distance in half and have important implications for the seismic hazard of the San Diego-Tijuana metropolitan area (population ~3 million people).

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USGS1985

Reproduction and organochlorine contaminants in terns at San Diego Bay

In 1981, we studied Caspian Terns (Sterna caspia) and Elegant Terns (S. elegans) nesting at the south end of San Diego Bay, California. Randomly collected Caspian Tern eggs contained signficantly (P < 0.05) higher mean concentrations of DDE (9.30 ppm) than did Elegant Tern eggs (3.79 ppm). DDE may have had an adverse effect on Caspian Tern reproduction but the relationship between hatching success and DDE concentration was not clear. We found an unusually high incidence of chicks (4.6%) that died in hatching. Caspian Tern eggs that broke during incubation or contained chicks that died while hatching had shells that were significantly (P < 0.05) thinner than eggs collected before 1947, and DDE was associated with reductions in shell thickness index (i.e., lowered eggshell density). Fish brought to Caspian Tern chicks contained up to 3.0 ppm DDE and 1.1 ppm PCBs. Organochlorine concentration brains of terns found dead were not high enough to suggest such poisoning as a cause of death.

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USGS1975

Quaternary faults at San Diego Bay, California

Acoustic-reflection profiles of subbottom strata reveal numerous faults that cut Quaternary deposits within and directly outside of San Diego Bay. These faults, together with previously mapped onshore faults, constitute the Rose Canyon fault zone that forms the local west boundary of the Santa Ana tectonic block, which is bounded on the east by the Elsinore fault zone. The minor earthquakes that have been felt in San Diego during historic time and accurately recorded during the past 41 yr are too infrequent to explain the observed rate of slip. The principal faulting is inferred to take place during moderate earthquakes similar to previous ones recorded along the west side of the Santa Ana block in 1933 at Long Beach, Calif., and in 1956 at San Miguel, Baja California. The known magnitudes of these previous events suggest that earthquakes in San Diego could attain a magnitude of approximately 6.5. An offset of the coast at Point La Jolla, when divided by the offset associated with previously studied earthquakes of magnitude 6.5, suggests that such events occur there at an average of approximately once every 600 yr.

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