SR 144

by L.D. Porter, J.T. Ragsdale and R.D. McJunkin

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On 13 August 1978 a moderate magnitude earthquake (ML = 5.1, Cal Tech Seismological Laboratory) occurred in the ocean 6 km south of Santa Barbara, California. The earthquake, originating at 22:54:52:4 ±0.1 second (GMT), had a focal depth of 12.5 ±3 km and was located at latitude 34.37° N and longitude 119.72° W (±2 km) (Lee and others, 1978).

Building damage generated by the earthquake was generally moderate and consisted mostly of broken glass and plaster. The approximate area affected by the 13 August earthquake is shown in Figure 1.

The Santa Barbara area has a moderate extent of instrumentation which includes 27 accelerographs within 90 km of the epicenter (Figure 2). Eleven accelerographs were triggered by the 13 August main event: eight of these instruments belong to the California Division of Mines and Geology (CDMG), one belongs to the Southern California Edison Company, one to the U.S. Bureau of Reclamation and one to the U.S. Geological Survey. Three CDMG stations in the Santa Barbara area recorded motions significant enough to warrant digitization (Figure 3): (1) Santa Barbara-Freitas Building, (2) Santa Barbara-UCSB North Hall Building and (3) Santa Barbara-UCSB Goleta. This report presents analyzed data from records of earthquake motions at these stations. The graphics in this report include uncorrected accelerations, corrected accelerations, velocities and displacements, response spectra, Fourier Spectra, and velocity-response envelope spectra.

The Santa Barbara-Freitas Building and USCB North Hall stations are reinforced concrete shear wall buildings, instrumented with central recording systems (Kinemetrics model CRA-1) monitoring nine channels each. The Santa Barbara-UCSB Goleta freefield station is instrumented by a three-channel strong-motion recorder (Kinemetrics model SMA-1) housed in a lightweight prefabricated metal shop building on a concrete slab floor.

The highest peak ground and structure accelerations generated by the August earthquake were in the Santa Barbara-UCSB North Hall buildings; corrected peak accelerations expressed in gravity (g), are 0.40 g and 0.96 g in the north-south direction on the ground floor and roof, respectively. Corrected peak ground accelerations from the Santa Barbara-UCSG Goleta freefield site, located approximately 1250 m northwest of UCSR North Hall, are 0.35 g north-south, 0.29 g east-west and 0.14 g vertical. The corrected peak accelerations are maximum in the east-west direction at the Santa Barbara-Freitas building and registered 0.23 g in the basement and 0.65 g on the roof.