Earthquakes are among the most dynamic, and common, of geologic phenomena.  More than a million earthquakes occur worldwide each year.  In California, seismologists (geologists who specialize in studying earthquakes) record more than 1000 discrete events each month; or more than 12,000 a year!  Earthquakes are a manifestation of the dynamic nature of the Earth’s fragmented and mobile crust.  As Earth’s major tectonic plates collide, separate, or slide past one another they fracture the rocks making up the Earth’s crust.  That sudden fracture or rupture releases energy in the form of seismic waves.  Those waves propagate outward in all directions – Earthquake!  Of course, the nearer you are to the event – the point of rupture is called the focus – the more likely it is that you will “feel” the earthquake. 

Fortunately, most events are “not felt” by people.  But while large magnitude events are relatively rare, their impact on human society can be great.  The 1994 Northridge, California, earthquake killed 57 people and injured nearly 11,000 more.  In the nearby San Fernando Valley, overpasses fell, bridges collapsed, and hundreds of homes and buildings were damaged.  Damages totaled nearly 12.5 billion dollars!

Great Sumatra-Andaman Earthquake.   But the death and destruction at, Northridge pales in comparison to the Great Sumatra-Andaman Earthquake of 26 December 2004.  This earthquake occurred offshore of Sumatra, Indonesia, along the intersection of two of Earth’s tectonic plates, the India and Burma plates.  Locally, sections of the seafloor rose 15-meters, that’s 45 feet.  Disruption of the sea floor, and the overlying water column, generated a large, fast-moving tsunami – with a velocity of up to 600 miles per hour.  The tsunami came ashore throughout the Indian Ocean basin and was in places more than 30-meters high (100 ft – or the equivalent of a 10-story building).  It was directly responsible for the deaths of 225,000 people in 11 countries bordering the Indian Ocean, making it the greatest natural disaster of the 21st Century to date. 

Arizona Earthquakes.  Large earthquakes in Arizona are rare, but not unheard of.  See the attached map for the distribution of large historical earthquakes in Arizona.  The Colorado Plateau of northern Arizona is particularly prone to moderate-sized earthquakes.  Dave Brumbaugh of Northern Arizona University maintains a network of seismometers (a device to sense and record the ground acceleration associated with earthquakes) to monitor activity there. 

Yuma, Arizona, situated in the southwestern-most corner of Arizona, is at high-risk from powerful earthquakes from the nearby San Andreas Fault and its splay faults, the Imperial and Algodones faults.   In 1979, rupture along the Imperial fault produced a powerful, magnitude  6.4 event, sending surface waves (Love and Rayleigh waves) racing towards Yuma, 70 miles to the east.  Observers in Yuma reported the ground rising and falling before them, in a manner similar to water wave behavior in oceans and lakes.

File(s) Available for Download:

1887 | Sonoran Earthquake - "Not Our Fault"

1888 | Summary of Earthquake Activity in 1888

1889 | Summary of Earthquake Activity in 1989

1979 | Earthquakes of 1979

1980 | Casa Grande Bulge Cause Earthquakes in 1980

1990 | Toroweap Fault in 1990

1990-1991 | Summary of Earthquake Activity, 1990 and 1991

1991 | Horseshoe Fault in 1991

1992 | Landers Earthquake Sequence

1992 | St. George Earthquake in 1992

1993 | Seismic Hazard in Arizona in 1993

1994 | Arizona Earthquakes in 1994

1996 | Seismic Hazard in Flagstaff Area - 1996

2000 | Earthquake Hazards in Arizona

Summary of Earthquakes Causing Damage in Arizona