Glossary


0-9
1868 Hayward
A magnitude 6.8 earthquake, in Hayward. 30 people were killed.

1906 San Francisco
A magnitude 7.8 earthquake, 5 miles from San Francisco. 3000 people were killed.

1925 Santa Barbara
A magnitude 6.8 earthquake, 9 miles from Santa Barbara. 13 people were killed.

1933 Long Beach
A magnitude 6.4 earthquake, in Long Beach. 115 people were killed.

1952 Kern County
A magnitude 7.3 earthquake, 25 miles from Bakersfield. 12 people were killed.

1971 San Fernando
A magnitude 6.6 earthquake, 8 miles from San Fernando. 65 people were killed.

1987 Whittier Narrows
A magnitude 5.9 earthquake, 9 miles from downtown Los Angeles. 8 people were killed.

1989 Loma Prieta
A magnitude 6.9 earthquake, 9 miles from Santa Cruz. 63 people were killed.

1994 Northridge
A magnitude 6.7 earthquake, in Northridge. 60 people were killed.

2003 San Simeon
A magnitude 6.6 earthquake, 23 miles from Paso Robles. 2 people were killed.

2014 South Napa, South Napa
A magnitude 6.0 earthquake, 6 miles from Napa. 1 person was killed.

B
Blind Zone, Blind Zones
A region, centered on the epicenter, where no warning is provided before serious ground motions arrive. A few seconds of delay producing a warning can produce a Blind Zone covering 400 square miles.

Brawley, Brawley Fault Zone
A seismically active area in the northern part of Imperial County responsible for many swarms and moderate earthquakes.

C
Calaveras, Calaveras Fault
This SF Bay Area fault has a 7% in 30 years chance of producing a magnitude 6.7 or greater earthquake.

CREWS
The Coachella Valley Regional Earthquake Warning System.

E
Elsinore, Elsinore Fault
This Southern California fault has a 11% in 30 years chance of producing a magnitude 6.7 or greater earthquake.

epicenter
The location on the surface directly above the point deep in the earth, called the Hypocenter, where the earthquake starts.

EWS
An Earthquake Warning System (EWS) uses ground motion sensors to detect and analyze an earthquake and initiate actions to protect people and equipment.

F
false alarm, false alarms
When a protective action is taken even though the required conditions, such as shaking intensity, did not occur.

focus
The point deep in the earth where the earthquake starts. The epicenter is directly above it on the surface. Also called the hypocenter.

G
Garlock, Garlock Fault
This fault has a 6% in 30 years chance of producing a magnitude 6.7 or greater earthquake.

GFLOP, GFLOPs
billion floating point operations per second

GMAC, GMACs
billion multiply-accumulate operations per second

H
Hayward-Rodgers Creek, Hayward-Rodgers Creek Fault
This fault system has a 31% chance in 30 years of a magnitude 6.7 or greater earthquake.

hypocenter
The point deep in the earth where the earthquake starts. The epicenter is directly above it on the surface. Also called the focus.
See also: epicenter

I
ICREWS
The Imperial County Regional Earthquake Warning System.

Imperial, Imperial Fault
A fault in southern Imperial County that produced several magnitude 6.0 and larger earthquakes in the last 100 years.

intensity
Describes how violently the ground shakes during an earthquake.

M
magnitude
Describes the total amount of energy released by an earthquake.

missed alarm, missed alarms
When a protective action is not taken even though the required conditions, such as shaking intensity, did occur.

MMI, Modified Mercalli Intensity
A qualitative scale of shaking intensity that uses observed effects to describe severity. The scale goes from MMI I (not felt) to MMI X+ (extreme damage).
For more information, see: What is MMI?

N
notification, notifications
An announcement of an earthquake that does not reliably occur before the arrival of serious ground shaking. Cannot be used to initiate critical responses.

NSAF, Northern San Andreas, Northern San Andreas Fault
This section of the San Andreas Fault, which runs from Hollister to Cape Mendocino, has a 21% probability of producing a magnitude 6.7 or greater earthquake in the next 30 years.

P
P-wave, P-waves
Primary, or P, waves are the fastest moving waves produced by an earthquake and are first to arrive. They do not carry much energy and cause only slight shaking.

Q
QuakeGuard Network
A network of seismic stations, based on the latest generation of QuakeGuards, to provide earthquake warning in California.

QuakeGuard, QuakeGuards
Our earthquake warning product capable of initiating alerts and protective actions for every earthquake, even at the epicenter.

R
red-tag, red-tagged
Buildings that are damaged too severely to be re-occupied are "red-tagged". Many of these are ultimately demolished.

Ring of Fire
Describes the borders of the Pacific Ocean. 90% of the world's earthquakes and 75% of the world's volcanoes are here.

rupture
A slip along a fault. The length of the slip is related to the earthquake's magnitude. A large earthquake can cause a rupture along hundreds of kilometers.

S
S-wave, S-waves
Secondary, or S, waves are the first waves to arrive from an earthquake that are large enough to cause damage. They are slower than P-waves but cause much greater shaking.

SAF, San Andreas, San Andreas Fault
The longest fault in California has a 59% in 30 years in Southern California and a 21% chance in Northern California of producing a magnitude 6.7 or greater earthquake.

SAF, Southern San Andreas, Southern San Andreas Fault
This section of the San Andreas Fault, which runs from Parkfield to Bombay Beach at the Salton Sea, has a 59% chance of producing a magnitude 6.7 or greater earthquake in the next 30 years.

San Jacinto, San Jacinto Fault Zone
This fault system has a 31% in 30 years chance of a magnitude 6.7 or greater earthquake.

seismometer, seismometers
device that measures ground motions, typically acceleration or velocity

SSAF, Southern San Andreas, Southern San Andreas Fault
This section of the San Andreas Fault, which runs from Parkfield to Bombay Beach at the Salton Sea, has the highest probability of producing a magnitude 6.7 or greater earthquake in the next 30 years.