Saturday, May 15, 2010

Seeing the Hayward Fault

Looking for something interesting to do while it was all foggy this morning, my mom and I went on a short walk around Hayward to look at one of the best examples of creep along the Hayward fault at the intersection of Rose and Prospect St. The Hayward fault is one of a few faults that separate the Pacific plate from the North American plate and it runs along the east side of the San Francisco Bay along the base of the hills. The San Andreas fault is one of the more famous faults that also is part of the fault system that marks the separation of the two plates.

The Hayward fault has been responsible for large earthquakes in the past, rivaling those caused by the San Andreas, and it has been deemed as more dangerous than the San Andreas fault by seismologists in the Bay Area because it has a higher chance of rupture. We actually live less than a mile away from it! Isn't that scary? It runs right underneath the Mormon Temple up the hill from our place.

Hayward Fault
Sidewalk shifted at Rose and Prospect St in Hayward, CA.

Anyways, at Rose and Prospect St, the Hayward fault runs right under your feet. The sidewalks and asphalt on the road there has been repaired many times due to the constant shifting of the earth underneath it, but one corner has remained untouched since the late 1960s when the concrete was poured. We walked over to that corner to see what the creep did to the sidewalk over the past 40-ish years.

Jenn 5/15/2010
Sitting on the North American plate Rose and Prospect St in Hayward, CA.

As you can see, the corner that sits on the North American plate has slid past the section of the curb that sits on the Pacific plate. When the concrete was poured, the sidewalk was even with the curb! The amount of creep that you can see on the curb is much smaller than the amount of sliding that the actual plates are doing, or want to slide past each other. Therefore, stress is building up and eventually, once the strength of the rock is exceeded, the fault will slip and cause a major earthquake. If you don't believe me, check this page out. It shows pictures of the curb taken roughly every 10 years since 1971. You can see how it moved over time! Somebody painted two black arrows in the spring of 2006 which were touching, but now you can see they have been shifted by a few millimeters since then. Whats crazy is that there are really nice houses built right next to the fault! Who would want to live there!?