The Loma Prieta, California, Earthquake of October 17, 1989—Tectonic Processes and Models

If there is a single theme that unifies the diverse papers in this chapter, it is the attempt to understand the role of the Loma Prieta earthquake in the context of the earthquake “machine” in northern California: as the latest event in a long history of shocks in the San Francisco Bay region, as an incremental contributor to the regional deformation pattern, and as a possible harbinger of future large earthquakes.

One of the surprises generated by the earthquake was the rather large amount of uplift that occurred as a result of the reverse component of slip on the southwest-dipping fault plane. Preearthquake conventional wisdom had been that large earthquakes in the region would probably be caused by horizontal, right-lateral, strike-slip motion on vertical fault planes.

In retrospect, the high topography of the Santa Cruz Mountains and the elevated marine terraces along the coast should have provided some clues. With the observed ocean retreat and the obvious uplift of the coast near Santa Cruz that accompanied the earthquake, Mother Nature was finally caught in the act. Several investigators quickly saw the connection between the earthquake uplift and the long-term evolution of the Santa Cruz Mountains and realized that important insights were to be gained by attempting to quantify the process of crustal deformation in terms of Loma Prieta-type increments of northward transport and fault-normal shortening.

This publication consists of the following articles:

• Introduction, by Robert W. Simpson

• Relations between folding and faulting in the Loma Prieta epicentral zone: Strike-slip fault-bend folding , by John H. Shaw, Richard E. Bischke, and John Suppe

• Geologic assessment of the relative contribution of strike-slip faulting, reverse-slip faulting, and bulk squeezing in the creation of the central Santa Cruz Mountains, California, by Gianluca Valensise

• Complex fault interactions in a restraining bend on the San Andreas fault, southern Santa Cruz Mountains, California, by Susan Y. Schwartz, Daniel L. Orange, and Robert S. Anderson

• Earthquake-induced static-stress changes on central California faults, by Robert W. Simpson and Paul A. Reasenberg

• Cumulative slip along the peninsular section of the San Andreas fault, California, estimated from two-dimensional boundary-element models of historical rupture, by Paul Bodin and Roger Bilham

• Three-dimensional lithospheric kinematics in the Loma Prieta region, California: Implications for the earthquake cycle, by Kevin P. Furlong and David Verdonck

This publication is part of the set of four multi-chapter USGS Professional Papers on the Loma Prieta, California, Earthquake of October 17, 1989:

Professional Paper 1550, Earthquake Occurrence , Coordinators: William H. Bakun and William H. Prescott

Professional Paper 1551, Strong Ground Motion and Ground Failure, Coordinator: Thomas L. Holzer

Professional Paper 1552, Performance of the Built Environment, Coordinator, Thomas L. Holzer

Professional Paper 1553, Societal Response, Coordinator: Dennis S. Mileti