On March 11, 2011, at 2:46 p.m. local time (05:46 Universal Time, or UTC), a magnitude 8.9 earthquake struck off the east coast of Japan, at 38.3 degrees North latitude and 142.4 degrees East longitude. The epicenter was 130 kilometers (80 miles) east of Sendai, and 373 kilometers (231 miles) northeast of Tokyo. If initial measurements are confirmed, it will be the world’s fifth largest earthquake since 1900 and the worst in Japan’s history.

This map shows the location of the March 11 earthquake, as well as the foreshocks (dotted lines) and aftershocks (solid lines). The size of each circle represents the magnitude of the associated quake or shock. The map also includes land elevation data from NASA’s Shuttle Radar Topography Mission and ocean bathymetry data from the British Oceanographic Data Center.

According to the U.S. Geological Survey (USGS), the earthquake occurred at a depth of 24.4 kilometers (15.2 miles) beneath the seafloor. The March 11 earthquake was preceded by a series of large foreshocks on March 9, including an M7.2 event. USGS reported that the earthquakes “occurred as a result of thrust faulting on or near the subduction zone interface plate boundary.”

The March 11 quake sent tsunami waves rushing into the coast of Japan and rippling out across the entire Pacific basin. Crescent-shaped coasts and harbors, such as those near Sendai, can play a role in focusing the waves as they approach the shore. Also, since land elevation is low and flat along much of the Japanese coast, many areas are particularly vulnerable to tsunamis.

The Japan Meteorological Agency reported maximum tsunami heights of 4.1 meters at Kamaishi at 3:21 p.m. (06:21 UTC), 7.3 meters at 3:50 p.m. (06:50 UTC) at Soma, and 4.2 meters at 4:52 p.m. (07:52 UTC) at Oarai.

The U.S. Pacific Tsunami Warning Center (PTWC) reported a wave with maximum height of 2.79 meters (9.2 feet) at an observing station at Hanasaki, Hokkaido, at 3:57 p.m. local time (06:57 UTC). Other PTWC reports:

• 1.27 meters (4.2 feet) at 10:48 UTC at Midway Island
• 1.74 meters (5.7 feet) at 13:72 UTC at Kahului, Maui, Hawaii
• 1.41 meters (4.6 feet) at 14:09 UTC at Hilo, Hawaii
• 0.69 meters (2.3 feet) at 15:42 UTC in Vanuatu
• 1.88 meters (6.2 feet) at 16:54 UTC at Port San Luis, California
• 2.02 meters (6.6 feet) at 16:57 UTC at Crescent City, California

1. References

2. Japan Meteorological Agency (2011, March 11). Latest Tsunami Information. Accessed March 11, 2011.
3. Pacific Tsunami Warning Center (2011, March 11). Tsunami Messages for the Pacific Ocean. Accessed March 11, 2011.
4. U.S. Geological Survey (2011, March 11). Magnitude 8.9 - Near The East Coast of Honshu, Japan. Accessed March 11, 2011.

NASA Earth Observatory image created by Robert Simmon and Jesse Allen, using earthquake and plate tectonics data from the USGS Earthquake Hazard Program, land elevation data from the Shuttle Radar Topography Mission (SRTM) provided by the University of Maryland’s Global Land Cover Facility, and ocean bathymetry data from the British Oceanographic Data Center’s Global Bathmetric Chart of the Oceans (GEBCO). Caption by Michael Carlowicz.