Science Spotlight

Station P496

Researcher: Ken Hudnut
U.S. Geological Survey

When a big earthquake happens, I get to venture out and do field work, which is what I love most of all about my job.

P496 is located near McCabe Elementary and High Schools in El Centro, California.

State: CA
Country: United States
Elevation: -40.1 m
Lat/Long:  32.7506 / -115.596

El Mayor-Cucapah Earthquake

P496 is a site that moved permanently as a result of the 2010 El Mayor-Cucapah earthquake. It lurched violently, and since then has continued to move at a rate faster than the usual background rate of plate tectonic movement. It moved again, but only by a little bit, in the 2012 Brawley Earthquake Swarm. This swarm included hundreds of small and medium sized earthquakes. The movement between the earthquakes, as well as the dynamic movements during earthquakes and the early postseismic deformation, all tell us more about how faults and earthquakes work.

During the 2010 earthquake the P496 station moved by more than 16 cm even though this station is a distance of over 60 km from the earthquake epicenter and 15 km away from the northern extent of the rupture. Smaller displacements were measured throughout southern California.

The displacement of PBO site P496 at the time of the El Mayor-Cucapah earthquake, all on its own, would not be enough to teach us much about the earthquake. But the information from this and many other GPS stations, plus the fault rupture data and seismological network data, were all combined with satellite imagery to form a complete study of the earthquake source (abstract, full paper). This study showed that although the map view of the earthquake looked like a simple linear source, at depth the earthquake was very complex. It started out small, then went big as the rupture jumped from one fault section to the next in a cascading rupture process.

Figure 1. Ken Hudnut (center) with CICESE colleagues John Fletcher and Javier Gonzalez after the El Mayor-Cucapah magnitude 7.2 earthquake surface rupture initial aerial reconnaissance, April 6, 2010. This marked the start of a multi-year project resulting in comprehensive mapping and documentation of the extensive faulting associated with the earthquake.

Figure 3. Map showing the displacements during the El Mayor-Cucapah earthquake. The motion of P496 is highlighted in red. (Credit: Tom Herring, MIT)

Figure 5. Shaking from the earthquake, along with the fault rupture. Credit: Southern California Seismic Network


Figure 2. Part of the surface rupture from the El Mayor-Cucapah magnitude 7.2 earthquake, taken from a helicopter. (Photo: Ken Hudnut)

Figure 4. Positions of P496 calculated 5 times per second during the earthquake. The east, north, and vertical traces are offset to allow you to see them better. (Credit: Kristine Larson).

Figure 6. Position changes for P496 in a North American fixed reference frame. (For help interpreting the graphs, see the GPS Data page.)

Spotlight Questions

  • How much did the ground move during the El Mayor-Cucapah earthquake?
  • Look at this USGS plot of P496 data. What is different about it from the plot shown here? Why might it be helpful to look at the data this way?
  • UNAVCO helped respond to the El Mayor-Cucapah earthquake by providing GPS and other equipment, and by providing high-rate GPS data. Look at UNAVCO's event response page. How many different institutions contributed to collecting and sharing information about this earthquake? What are some benefits to having many institutions involved? What are potential drawbacks?

Last modified: 2019-12-26  16:24:51  America/Denver  


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