EQs & Dip-Slip Faults

Normal Faults

• Sierra Nevada fault
• March 27, 1872 Owens valley earthquake
• 8.5 M - California’s greatest
• 29 killed

Cities on normal faults include: Bishop, Reno, Carson City

Thrust faults

The southern boundary of the transverse range is a series of east trending thrust faults Santa Monica & Sierra Madre fault system. These faults may be characterized by very high horizontal acceleration

Cities on or very near thrust faults – Pasadena, all foothill communities

Blind Thrusts

Blind Thrust faults have no surface expression, so they are typically unknown until an earthquake occurs

Chino EQ - July 29, 2008

Time: Tuesday, July 29, 2008 at 11:42:15 AM Location: epicenter 4 km (3 miles) WSW from Chino Hills, CA Magnitude: 5.4 Type Of Faulting: a mixture of thrust and left-lateral strike-slip faulting Depth: 9 km Fault: Unknown at this time, but appears to be half-way in between the Whittier and Chino fault

Below are two seismic intensity maps. The one on the left is a USGS Community Internet Intensity Map, created by the public through the USGS's "Did You Feel It" site. Here, the public can fill out a form describing how strongly they felt the earthquake. This is useful to scientists as humans obviously feel events in ways that sensors can't. The CISN ShakeMap on the right was created by sensors. Sensors are more sensitive to slight movements and variations that human's can't perceive. Thus both types of maps can help seismologists better prepare for the next earthquake.

1971 San Fernando Earthquake

Time: February 9, 1971, 6:01 am PST

Magnitude: Mw 6.6; Intensity: XI

Depth: 8.4 km

Length of shaking: 60 seconds!

Type of faulting: thrust

Fault involved: San Fernando Fault Zone; Minor offset reported on the eastern Santa Susana Fault Zone

Damage

• Over $500 million in property damage
• Several hospitals suffered severe damage
• Newly constructed freeway overpasses also collapsed
• 65 deaths
  • Loss of life would have been greater had the EQ struck later in the day.

Results

• Building codes were strengthened
• Alquist Priolo Special Studies Zone Act was passed in 1972.
  • The purpose of this act is to prohibit the location of most structures for human occupancy across the traces of active faults and to mitigate thereby the hazard of fault rupture.
  • Visit http://www.quake.ca.gov/gmaps/WH/regulatorymaps.htm to find out if your home is in an AP Zone!

1994 Northridge Earthquake

Time: January 17, 1994, 4:30:55 Am PST Location: 20 Miles West-northwest of Los Angeles, 1 Mile South-southwest of Northridge Magnitude: Mw 6.7 Type Of Faulting: blind thrust Fault involved: Northridge Thrust Depth: 18.4 Km Duration of shaking: 10-20 seconds The earthquake significantly deformed the Earth’s crust over an area of about 4,000 square kilometers Santa Susana Mountains were pushed up by at least 40 cm Northridge uplifted at least 20 cm Other areas 20-40 cm

Damages

• Ground failures of many types at distances up to about 90 kilometers from the epicenter
• Surface Ruptures
• Landsliding
• Soil Liquefaction