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6/12/2005 Anza Earthquake

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Information from the CISN
Date & Time (Local): 2005/06/12
08:41:46 (PDT)
Date & Time (UTC): 2005/06/12
15:41:46 (UTC)
Location: 9 km (6 miles) ESE of Anza, CA
33.533 -116.578
Depth (km): 14.1
Mw: 5.2

Details

Map of
seismicity near Anza June 13, 07:00 PDT:

The magnitude of the earthquake was revised from its preliminary estimate of ML5.6 to Mw5.2.

June 12, 14:00 PDT:

A local magnitude M5.2 earthquake occurred 9 km (6 miles) east-southeast of Anza, California at 8:41 am on Sunday, 12th of June 2005. The mainshock focal depth was 13 km (8 miles). The earthquake is located within the San Jacinto fault zone and within the Anza "gap" (where future M>6 events are expected). The earthquake was widely felt across all of southern California and into Nevada and Arizona. The strongest shaking occurred to the northwest of Anza, about 25 km (15 miles) to the south of Palm Springs.

The earthquake probably occurred on a small "cross fault" within the San Jacinto system. A "cross fault" is a small fault at a high angle to the main fault, that accomplishes the same overall strain. The San Jacinto fault strikes northwest with right-lateral strike-slip motion, while the alignment of aftershocks to the M5.2 suggests a northeast strike to its fault. The depth of the earthquake is 13 km. This depth puts the earthquake below the section of the fault thought to be accumulating slip for a large future earthquake.

The San Jacinto fault is a 200 km long branch of the San Andreas system that accommodates horizontal motion between the North America and Pacific Plates. The past history of the region includes numerous M5 events, including a M5.1 on 31st of October 2001 and a M6.0 earthquake that occurred in 1937, located about 10 miles to the southeast of today's epicenter.

The San Jacinto fault is the most active earthquake fault in California, producing an earthquake of at least 6 eight times in the last century, including:

Egill Hauksson and Lucy Jones

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Ground Motions

The CISN Southern California Management Center produces ShakeMaps for events of M3.5 and higher. ShakeMaps are based on the observed ground motions from seismic instruments combined with predicted motions in areas without sensors.

The CISN Engineering Data Center produces reports showing details of ground motions for events of interest. The have issued an Internet Quick Report (IQR) for the M5.2 showing records from Idyllwild (27 km away) as well as other sites of interest:

The M5.2 was widely felt in southern California. People with Internet access can report their observations of shaking and damage through the Did You Feel It? Web site. In the links below, you can see the maps illustrating the reported intensities for several events in this sequence. Unlike the ShakeMaps - which are based on data from seismic instruments - these maps are based on human observations. You can contribute to these data by filling out the form for each event.

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Maps

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Waveforms

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Related Links

CISN Earthquake Reports


California Integrated Seismic Network
cisninfo@cisn.org

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