{"id":1435,"date":"2014-03-28T20:44:18","date_gmt":"2014-03-29T04:44:18","guid":{"rendered":"http:\/\/earthjay.com\/?p=1435"},"modified":"2014-03-28T20:44:18","modified_gmt":"2014-03-29T04:44:18","slug":"m-5-1-earthquake-in-la-habra","status":"publish","type":"post","link":"https:\/\/earthjay.com\/?p=1435","title":{"rendered":"M 5.1 earthquake in La Habra"},"content":{"rendered":"

All Right!
\nA good sized shaker (nice and small) just happened near La Habra in southern CA. Here is the USGS<\/a> web site for this earthquake. Here<\/a> is some general information about earthquakes in southern CA. This is a really shallow earthquake at 1.9 km!
\nBased on reports from my family that live a few miles from the epicenter, they are shaken but not stirred.
\nHere is an early moment tensor<\/a>. It looks like this is an oblique strike-slip\/reverse earthquake. It probably shook pretty strongly there.
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\nHere is a shaking intensity map based on a model of the earth and the magnitude of the earthquake. The colors represent shaking intensity using the Modified Mercalli Shaking Intensity Scale.
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\nHere is a map showing some aftershocks. It appears that this may be a rupture on a northeast striking fault. A combination of a strike-slip earthquake and a thrust (compressional) earthquake. The hills north of Brea and La Habra are formed along the Whittier fault in the Elsinore fault zone, which is a sister fault system to the San Andreas fault system (a plate boundary transform fault system). If you click on the map, it will open an updated map that shows the main shock epicenter actually did change.
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\nBased on Danielle Verdugo Madugo<\/a>, Egill Hauksson thinks it is may be on the Puente Hills fault. Here is a map from Tucker and Dolan<\/a> (2001). The Puente Hills blind thrust fault appears to be responsible for the uplift associated with the Coyote Hills east of La Mirada. The Puente Hills fault ruptured in 1987 with a M 6.0 earthquake. Here is a great paper by Leon et al. 2007<\/a> that describes the tectonics of the Puente Hills fault as it relates to seismic hazard.
\nHere is map and cross section showing the location of the 1987 M 6.0 “Whittier Narrows” earthquake. (A) Map showing Brea and downtown LA as they relate to the epicenter. The lighter shaded polygons are their estimates of the location of thrust fault planes as they dip to the north. The fault tips are the thick black lines. (B) The cross sectional view of the crust in this region. The cross section locations are located in (A) by the blue lines from B-B1-B2. There is a break in the cross section at B1.
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\nThe 1987 Whittier Narrows earthquake (i remember that one) is located at a depth of ~13 km. Tonight’s earthquake is also shallow, at about 8 km as i post this. The Whittier fault is marked by the “WF.” The 1987 EQ was north of the WF. Tonight’s earthquake would be up-dip of the 1987 earthquake, and further east. There are lots of faults in this region, so it is pretty complicated. Here is a map from Shaw et al. (2002)<\/a> showing the different segments of the Puente Hills fault system.
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\nHere is another cross section, from the Shaw paper, that shows where Santa Fe Springs and Montebello are. This cross section is west of today’s M 5.1 earthquake.
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\nThese are the seismic data Shaw et al. (2002) used to interpret their cross section above.
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\nBased on the USGS web page:
\n“There have been 23 aftershocks as of 10:00PM on March 28, the largest of which was a M3.6 at 9:30PM, and was felt locally near the epicenter. The aftershock sequence may continue for several days to weeks, but will likely decay in frequency and magnitude as time goes by.
\nHere is a cool video from SCEC<\/a>
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