Posted 468 days ago – U.S. Geological Survey
An earthquake with magnitude 5.8 occurred near Wakayama, Honshu, Japan at 20:33:17.59 UTC on Apr 12, 2013. (This event has been reviewed by a seismologist.)
- Expect aftershocks. These secondary shockwaves are usually less violent than the main quake but can be strong enough to do additional damage to weakened structures and can occur in the first hours, days, weeks, or even months after the quake.
- Look for and extinguish small fires. Fire is the most common hazard after an earthquake.
- Be aware of possible tsunamis if you live in coastal areas. These are also known as seismic sea waves (mistakenly called "tidal waves"). When local authorities issue a tsunami warning, assume that a series of dangerous waves is on the way. Stay away from the beach.
- Be careful when driving after an earthquake and anticipate traffic light outages.
- What to do after an earthquake.
What is an earthquake?
Earthquakes with magnitude of about 2.0 or less are usually called microearthquakes; they are not commonly felt by people and are generally recorded only on local seismographs. Events with magnitudes of about 4.5 or greater - there are several thousand such shocks annually - are strong enough to be recorded by sensitive seismographs all over the world. Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On the average, one earthquake of such size occurs somewhere in the world each year.
Magnitude measures the energy released at the source of the earthquake as determined from measurements on seismographs. An earthquake has one magnitude. The magnitude scale most commonly in use now is called the moment magnitude scale. Moment is a physical quantity proportional to the slip on the fault times the area of the fault surface that slips; it is related to the total energy released in the EQ. The moment magnitude provides an estimate of earthquake size that is valid over the complete range of magnitudes, a characteristic that was lacking in other magnitude scales.
Intensity measures the strength of shaking produced by the earthquake at a certain location. Intensity is determined from effects on people, human structures, and the natural environment. An earthquake can produce shaking of many different intensities. The Modified Mercalli Intensity Scale is used in the US.
Source U.S. Geological Surveyearthquake.usgs.gov