Science Spotlight

Station P224


Researcher: Roland Bürgmann
University of California, Berkeley

As a kid, I always liked science, but didn't really think of it as a job possibility. It seemed like science was something you do for fun, not for work.


P224 helps scientists understand both earthquakes and "creep" along the Hayward fault in the San Francisco Bay area.


Name: SIBLEYVOLC
State: CA
Country: United States
Elevation: 407.4 m
Lat/Long:  37.8639 / -122.2191

Hayward Fault

We may think of the San Andreas Fault as the contact between the Pacific plate and the North American plate, where the Pacific plate moves northwestward past the North American continent. But the San Andreas Fault isn't the only fault accommodating, or allowing, this motion between the plates.

P224 is located just east of the Hayward Fault, a fault running parallel to the San Andreas Fault in the San Francisco Bay area in California. GPS sites west of the both the San Andreas Fault and the Hayward Fault are moving northwest relative to stable North America (Figure 2). P224, on the North American side of the Hayward Fault, also moves to the northwest. Even relative to the Sierra Nevada, there is still some motion, showing that the Bay Area faults to the east of the Hayward Fault are also active. Plate motion doesn't happen all along one single fault. It affects a plate boundary zone, which can extend deep into a continent.

If we compare the motion of P224 with station P181 located across the Hayward Fault (Figure 1), we can see that the relative velocity between the stations is about 9 mm per year. Given the location of the stations, this suggests that the slip rate on the fault must be close to this number.

The Hayward Fault is one of our most important research targets in the San Francisco Bay Area. The fault had a large (magnitude ~7) earthquake in 1868, but also creeps, or slips steadily by a few mm each year, on substantial portions of the fault surface. We use GPS data from P224 and other stations to estimate the slip rate on the Hayward Fault, and to determine where the fault is creeping and where it is locked.

To explore the Hayward Fault in Google Earth, check out the USGS Active Traces of the Hayward Fault virtual tour.

Figure 1. Position changes for P224 (black) and P181 (blue) in a North American fixed reference frame. (For help interpreting the graphs, see the GPS Data page.)


Figure 3. A curb offset by "creep" along the Hayward fault. The offset is not from a large earthquake, but rather from frequent, small amounts of slip along the fault. (Credit: Sue Hirschfeld, California State University, via USGS)

 

Figure 2. Velocities of GPS sites in the San Francisco Bay area. Blue arrows show motions for sites in the Bay Area Regional Deformation (BARD) network; yellow arrows show motions for sites in the Plate Boundary Observatory (PBO) network and sites occupied periodically rather than continuously, called campaign sites. Faults are shown as black lines. The velocities for P224 and P181 have been highlighted in red.

Spotlight Questions

  • Are P224 and P181 moving in the same direction? Are they moving at the same rate? Which site is moving faster? Is this what you would expect, based on where the sites are located relative to the Hayward Fault?

Last modified: 2019-12-26  16:24:52  America/Denver  

 

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