Natural Hazards

There is no pattern in California of large, damaging earthquakes occurring more frequently during periods of heavy precipitation or periods of drought. Therefore, it’s unlikely that seismic hazard is affected by precipitation. This makes sense as rainwater cannot easily percolate several kilometers below the earth's surface to the depths where most earthquakes occur. However, periods of heavy...

Debris flows are fast-moving landslides that are particularly dangerous to life and property because they move quickly, destroy objects in their paths, and often strike without warning. They occur in a wide variety of environments throughout the world, including all 50 states and U.S. Territories. Debris flows generally occur during periods of intense rainfall or rapid snowmelt and usually start...

The USGS issues ShakeAlert® Messages but alert delivery will come by other public and private means (internet, radio, television, cellular), including Wireless Emergency Alerts (WEA) -- think of an AMBER Alert -- delivered by FEMA’s Integrated Public Alert and Warning System (IPAWS). Alert delivery via the WEA system is available in California, Oregon, and Washington. To ensure that you can...

In addition to naturally occurring earthquakes, human activities such as mining and construction blasts can sometimes produce seismic waves large enough to be detected on the USGS national seismic network. These artificially-generated events have a different seismic ‘fingerprint’ from tectonic earthquakes, so they can be discerned by a seismologist when reviewed. Specifically, small quarry blasts...

The USGS operated the Geospatial Multi-Agency Coordination (GeoMAC) website from 2000-2020. GeoMAC was the public face of all wildland fire perimeters. That site was shut down on April 30, 2020 and responsibility for wildfire information was transferred to the National Interagency Fire Center (NIFC). The GeoMAC mapping application at "geomac.gov" has been replaced by the National Fire Situational...

Faults vs. Fault Lines on a Map In order to answer this question, we first need to explain some basics about faults. Faults are different from fault lines. A fault is a three-dimensional surface within the planet that might extend up to the surface or might be completely buried. In contrast, a fault line is where the fault cuts the Earth's surface… if indeed it does. The most prominent faults in...

Sometimes. Earthquakes, particularly large ones, can trigger other earthquakes in more distant locations though a process known as dynamic stress transfer/triggering. This means that the energy from the seismic wave passing through can cause a new earthquake, usually in already vulnerable locations prone to frequent earthquakes (e.g., volcanic regions). Examples of large events that triggered...

Most volcanic eruptions occur near the boundaries of tectonic plates, but there are some exceptions. In the interior of some tectonic plates, magma has been erupting from a relatively fixed spot below the plate for millions of years. As the plate continuously moves across that spot, a trail of progressively older volcanic deposits is left at the surface. The Hawaiian Islands are a good example of...

Most induced earthquakes are not directly caused by hydraulic fracturing (fracking). The recent increase in earthquakes in the central United States is primarily caused by disposal of waste fluids that are a byproduct of oil production. Wastewater disposal wells typically operate for longer durations and inject much more fluid than is injected during the hydraulic fracturing process, making them...

For the automated naming of earthquakes we use a GeoNames dataset to reference populated places that are in close proximity to a seismic event. GeoNames has compiled a list of cities in the United States where the population is 1,000 or greater (cities1000.txt). This is the primary list that we use when selecting nearby places. In order to provide the public with a better understanding for the...

Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault. Aftershocks occur near the fault zone where the mainshock rupture occurred and are part of the "readjustment process” after the main slip on the fault. Aftershocks become less frequent with time, although they can continue for days, weeks, months, or even years for a very large mainshock. A swarm, on the...

A nuclear explosion can cause an earthquake and even an aftershock sequence. However, earthquakes induced by explosions have been much smaller than the explosion, and the aftershock sequence produces fewer and smaller aftershocks than a similar size earthquake. Not all explosions have caused earthquakes. The range of a possible earthquake triggered by an explosion is limited to a few tens of...