California Earthquakes

Sylmar Earthquake About: When: 6:00 A.M. February 9, 1971 Where: San Fernando Valley What: Ruptured segment of the San Fernando Fault Zone. Magnitude 6.6

Damage 65 people died $500 million in damage Two hospitals were destroyed Freeway Interchange Collapsed

The Whittier Narrows Earthquake About: When: 7:42 A.M. October 1 st, 1987 Where: San Gabriel Valley What: Slip on a blind thrust fault. Magnitude 5.9 and 5.3

Damage 3 people died $358 million in damage

Loma Prieta Earthquake About: When: 5:04 P.M. October 17 th, 1989 Where: The greater San Francisco Bay Area What: Reflected seismic waves

Damage 63 people died & 3,757 were injured $6 billion in damage Cypress Street Viaduct San Francisco-Oakland Bridge

Northridge Earthquake About: When: 4:30 A.M. January 17 th, 1994 Where: San Fernando Valley What: Blind Thrust Fault

Damage 51 people died & 9,000 were seriously Injured $44 billion in damage 22,000 people left homeless, 25,000 dwellings uninhabitable, 9 hospitals lost, 9 parking garages collapsed, 9 bridges collapsed, portions of 11 major roads closed

Pictures

Total Damages and Costs  Over the past 23 years the costs of these 4 earthquakes has been a crushing blow for California  The total number of deaths is estimated to be 188  The total number of injuries is roughly estimated to be 8,804  The estimated costs of damage due to these earthquakes is $31,531,000,000

What Can Be Done?

Seismic Retrofitting  Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes.  The key elements of seismic retrofitting are the levels of modifications and the types of modifications

Levels of Modification  Public Safety: the number one goal is to ensure that in the event of an earthquake, a building will not fall on the people inside or the people passing by. Building will need to be replaced  Structure Survivability: Structure stays for so people can exit in the even of an earthquake. After the quake it will need extensive repair but no need for replacement.  Primary Structure Undamaged: Only cosmetic repairs necessary.  Structure Unaffected: Nothing damaged. Used for historic structures.

Types of Modification  Hybrid Solution: Ductile reinforcement and joining of rigid plates and beams  Isolation: Required for large masonry buildings. The building is separated from the actual foundation. The two are joined by steal or reinforced concrete beams.  Dampers: Absorb the energy of motion and turn it into heat. Helps to reduce the damage of the initial shock.  Reinforcement: Adding strength to the original structure. The most common form of Seismic retrofit.