Hayward Fault, California

by

Chris Jung

ES 767 Global Tectonics, Emporia State University

Figure 1. Photo of the Alameda Courthouse after the 1868 earthquake. Photo provided for use by the USGS.


Introduction
Tectonic Setting
1868 Earthquake
Three Dimensional Model
Conclusions
References


Introduction

The Hayward fault is a right-lateral strike-slip fault that runs parallel to the San Andres fault in northern California. It is approximately 72 kilometers long and trends NW across a densely populated area of California. The most notable earthquake that occurred along the fault was in 1868 and is named “the Great San Francisco earthquake” which was estimated to be a magnitude 7 earthquake. Damage estimates at the time were believed to be in the neighborhood of $350,000 (Brocher et al., 2008). Today the Hayward is considered to be extremely dangerous due to the high probability of an earthquake occurring and causing damage in the heavily developed area that has grown up around it.

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Tectonic Setting

The Hayward fault is one of several faults located on the west coast of the United States. It was formed by the intersection of the Pacific plate and the North American plate (Fig. 2). Movement of the Pacific plate is due to seafloor spreading at its divergent plate boundaries. When the Pacific plate encounters the North American plate subduction of the Pacific plate occurs. Where the plates intersect near the Hayward the plates are not subducted but instead form a transform boundary. A transform boundary is where two plates slide past one another.

Figure 2. Pacific plate and North American plate. Image provided for use by USGS.

At the Hayward fault the Pacific plate is moving towards the northwest and the North American plate is moving towards the southeast. The slight westward motion of the North American plate causes compressional forces that resulted in the formation of the fracture zone that includes the near vertical Hayward fault.

The Hayward fault is reported to have slipped at a rate of ~9 mm/yr and is overdue for a large earthquake event (Phelps et al., 2008). In recent history the primary damage from the fault has been caused by fault creep. Fault creep occurs when conditions in the rock allow the surface to slowly slide in response to building pressure deep in the fault. Fault creep has resulted in expensive damages to buildings, streets, and bridges along the fault. The USGS reports that the two sides of the Hayward are creeping by each other at 5 mm per year (State of California, 2010).

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1868 Earthquake

The most damaging earthquake to occur along the Hayward fault occurred on October 21, 1868. Seismographs were not around to record the earthquake but experts have estimated that it had a magnitude of 6.8. The initial earthquake lasted 40 seconds and had surface expressions along 20 miles of the Hayward fault. The average horizontal movement was determined to be 2 meters. Thirty deaths were reported in San Francisco along with over $350,000 (1868 dollars) in damages, making it one of the most destructive earthquake in United States history (Brocher et al., 2008)(Fig. 1).

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Interactive Model

The attached link is a three dimensional geologic model representing a 60 kilometers section of the Hayward fault. An interactive three dimensional map was created using Google SketchUp 7.1 and information obtained from a USGS three dimensional geologic map. The USGS map was constructed using faults to divide the lithology into fault blocks, which were then divided into stratigraphic column units and depositional surfaces (Phelps et al., 2008). Heavy faulting is apparent in the model but for the focus of this presentation the Hayward fault appears in translucent red.

Figure 3. Hayward Fault Map Units.

Figure 4. Hayward SketchUp model movie. After entering site push play and enter full screen mode (button on bottom left).

Figure 5. Aerial view of fault. Overlay was created using Landsat data.

Figure 6. East face of Hayward fault. Unit in green is the undifferentiated Great Valley Complex rock.

Figure 7. West face of Hayward fault. Note change from east side of fault.

Figure 8. Bottom view of fault.

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Conclusions

The Hayward fault has the potential to cause a devastating earthquake. Experts have predicted a large earthquake (7.0 magnitude or greater) could occur at anytime. The density of the population (~2.4 million residents) and large developments along the trace of the fault could make the next earthquake the most destructive and expensive in United States history (Brocher et al., 2008). Models like the one created by the USGS will aid in our understanding of the Hayward fault and improve methods for predicting earthquakes.

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References

Brocher, T., Boatwright, J., Lienkaemper, C., Schwatz, D., and Bundock, H. 2008.The Hayward Fault – Is It Due for a Repeat of the Powerful 1868 Earthquake? USGS Fact Sheet 2008 - 3019

Phelps, G., Graymer, R., Jachens, D., Ponce, D., Simpson, R., and Wentworth, C. 2008. Three-Dimensional Geologic map of the Hayward fault, northern California: Correlation of rock units with variations in seismicity, creep rate, and fault dip., p. 521-524 .

Phelps, G., Graymer, R., Jachens, D., Ponce, D., Simpson, R., and Wentworth, C. 2008. Three-Dimensional Geologic map of the Hayward fault Zone, San Francisco Bay Region, California.USGS Scientific Investigation Map 3045.

State of California. Department of Conservation, Hayward Fault Fact Sheet World Wide Web homepage http://www.conservation.ca.gov/index/Pages/HaywardFaultFactSheet.aspx [retrieved on April 17, 2010].

USGS Global Visualization Viewer. EROS, World Wide Web homepage http://glovis.usgs.gov/ [retrieved on April 21, 2010].

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This web page was created to fulfill the requirements for ES 776 Global Tectonics at Emporia State University.
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This page was created on 4/21/10.