Earthquake Epicenters - Natural Hazards in Arizona Viewer

Earthquakes occur when rocks comprising the Earth’s crust strain and rupture. This sudden release of ‘seismic’ energy can generate low, to moderate, to intense ground shaking. Severe ground shaking can collapse buildings, flatten bridges, initiate fires, and produce landslides, among other things. The epicenter is that point on the Earth’s surface where seismic energy first arrives.

Source: Arizona Geological Survey

Image: U.S. Geological Survey earthquake hazard map.

Earthquake epicenters displayed at the Natural Hazards in Arizona Viewer come from the Arizona Geological Survey Earthquake Catalog. The catalog represents just those earthquakes that have either been felt or recorded by a seismometer from 1852 to the present day.

Last Updated: AZGS Earthquake Catalog is updated frequently - daily, weekly, or monthly - to keep abreast of the most recent earthquake activity.

Related Information

•  Arizona is Earthquake Country – 44 pages
•  Earthquakes in Arizona: 1852-2011 – time-lapse video (90-seconds)
•  Arizona’s Earthquakes – An Overview  34 PowerPoint slide presentation
•  US Geological Survey Modified Mercalli Intensity Scale
•  The Lake Mary Fault: Potential Earthquake Threat of Flagstaff, Arizona (5-minutes)

Arizona has earthquakes. The entire state is susceptible to ground-shaking from time to time. The southwestern and northwestern corners of the state experience more earthquakes than the central or eastern part of the state. But large magnitude earthquakes that occur in neighboring states, i.e., California, Nevada, New Mexico, Colorado, and northern Mexico can also put Arizonans and their property at risk.
You can reduce earthquake-caused injuries and property damage by following these basic tips from the Arizona Dept. of Emergency Management and Military Affairs (https://ein.az.gov/hazards/earthquakes):

CHECK FOR HAZARDS IN THE HOME
•    Fasten shelves securely to walls;
•    Place large or heavy objects on lower shelves;
•    Store breakable items such as bottled foods, glass and china in low, closed cabinets with latches;
•    Hang heavy items such as pictures and mirrors away from beds, couches, and anywhere people sit;
•    Brace overhead light fixtures;
•    Repair defective electrical wiring and leaky gas connections, these are potential fire risks;
•    Secure a water heater by strapping it to the wall studs and bolting it to the floor;
•    Repair any deep cracks in ceilings or foundations. Get expert advice if there are signs of structural defects; and
•    Store weed killers, pesticides, and flammable products securely on bottom shelves in closed cabinets with latches.

IDENTIFY SAFE PLACES INDOORS AND OUTDOORS
•    Under sturdy furniture such as a heavy desk or table;
•    Against an inside wall;
•    Away from glass windows, mirrors, pictures, heavy bookcases, china buffets, or other furniture which could fall over; and
•    In the open, away from buildings, trees, telephone and electrical fires, overpasses, or elevated expressways.

EDUCATE YOURSELF AND FAMILY MEMBERS
•    Contact your local emergency management office or American Red Cross chapter for more information on earthquakes;
•    Teach children how and when to call 911, police, or fire department and which radio situation to tune to for emergency information;
•    Teach all family members how and when to turn off gas, electricity, and water;
•    Have disaster supplies on hand; and
•    Develop an Emergency Communication Plan and Emergency Supply Kit.

HELP YOUR COMMUNITY GET READY
•    Publish a special section in your local newspaper with emergency information earthquakes. Localize the information by printing the phone numbers of local emergency services offices, the American Red Cross, and hospitals;
•    Conduct a week-long series on locating hazards in the home; Work with local emergency services and American Red Cross officials to prepare special information for people with special needs on what to do during an earthquake; Provide tips on conducting earthquake drills in the home; Ask representatives of the gas, electric, and water companies about providing information regarding when and how to turn off utilities; and
•    Work together in your community and apply your knowledge to building codes, retrofitting programs, hazard hunts, and neighborhood and family emergency plans.

There is much that we know about earthquakes; and much we don’t know, but that’s another story. For example, we know that most earthquakes, but certainly not all, occur along the boundaries of tectonic plates, such as the tectonic boundary of the North American and Pacific tectonic plates (Fig. 1). We know that tectonic forces stress and strain (deform or bend) the rocks of the Earth’s crust, breaking and displacing those rocks. At the instant when the rock breaks, energy is released and radiates outward. The geometry of the fault, the nature of the rupture, and the properties of the surrounding rock and soil greatly influences the propagating energy wave and the amount of ground-shaking an area will experience. As seismic waves race through the Earth’s interior, they are refracted and reflected upon encountering rocks of different physical properties. We can model the velocity and direction of the propagating waves and trace their paths through the Earth’s interior.

We know large earthquakes release far more energy and are felt over correspondingly larger areas than small earthquakes. Earthquake waves diminish in intensity the further they travel, so the further you are from the epicenter (the point on the Earth’s surface where the earthquake wave first strikes) the less intense is the shaking from the earthquake. Most of the damage from earthquakes is associated with the side-to-side shaking that accompanies surface waves.

Prepare for aftershocks. The main shock or earthquake is always accompanied by aftershocks. Sometimes by thousands of aftershocks! And an earthquake that is sufficiently large to cause moderate to substantial damage is likely to be followed within minutes or hours by felt aftershocks. The January 17, 1994, M6.7 Northridge, California, earthquake was accompanied by more than 13,700 aftershocks, including two M6.0 events that followed within minutes to hours of the main event.

Following a large magnitude earthquake, be prepared for aftershocks and avoid damaged structures as they may be prone to collapse. And remember, aftershocks can occur for weeks, months, even years after a large earthquake as the Earth’s crust slowly returns to a state of rest.