A Caltech Library Service

A slow earthquake in the Santa Maria basin, California

Kanamori, Hiroo and Hauksson, Egill (1992) A slow earthquake in the Santa Maria basin, California. Bulletin of the Seismological Society of America, 82 (5). pp. 2087-2096. ISSN 0037-1106.

PDF - Published Version
See Usage Policy.


Use this Persistent URL to link to this item:


An M_L = 3.5 earthquake near Santa Maria, California, was recorded by the Southern California Seismic Network and a TERRAscope station at Santa Barbara (SBC) on 31 January 1991. The waveform of this event is dominated by 2- to 5-sec waves, and is different from that of ordinary events with similar size. Inquiries into operations in several oil fields in the area revealed that hydro-fracturing at a pressure of about 80 bars was being done at a depth of 100 to 300 m in the Orcutt oil field in the Santa Maria basin from about 9 to 11 a.m. on 31 January and the earthquake occurred in the afternoon. Field evidence of 30-cm displacement to a depth of 300 m was reported. The field evidence as well as the first-motion data indicates that the event had a thrust mechanism with the P axis in the NNE-SSW direction, which is in agreement with the regional stress field. From the analysis of the SBC record and the field evidence, we conclude that the source must be shallower than 1 km and the ratio of the radiated energy to the seismic moment is about 6.2 × 10^(-7), one to two orders of magnitude smaller than that of ordinary earthquakes. The occurrence of this earthquake demonstrates that release of regional tectonic stress in shallow sediments can yield significant seismic radiation at periods of a few seconds, the period range of engineering importance for large structures, and has important implications for excitation of long-period ground motions from large earthquakes in sedimentary basins.

Item Type:Article
Related URLs:
URLURL TypeDescription
Kanamori, Hiroo0000-0001-8219-9428
Hauksson, Egill0000-0002-6834-5051
Additional Information:© 1992 by the Seismological Society of America. Manuscript received 18 June 1992. We thank Charlie Catherman for providing us with the field data from the Orcutt oil field. We also thank Jim Mori for providing us with the record section of the Southern California Seismic Network, and William Savage and Marcia McLaren for providing us with the data obtained from the Seismic Network of the Pacific Gas and Electric Company. We thank Julie Shemeta for information on the well locations in the Orcutt oil field. This research was partially supported by the U.S. Geological Survey Grant 14-08-0001-G1774 and a grant from the L. K. Whittier Foundation. Contribution No. 5173, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California.
Group:Seismological Laboratory
Funding AgencyGrant Number
L. K. Whittier FoundationUNSPECIFIED
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5173
Issue or Number:5
Record Number:CaltechAUTHORS:20130425-141027388
Persistent URL:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38123
Deposited On:25 Apr 2013 21:43
Last Modified:09 Mar 2020 13:18

Repository Staff Only: item control page