Archives for: March 2011, 11
|USGS map showing location of Japan's magnitude 8.9 earthquake and aftershocks.|
The earthquake that devastated some parts of the Japanese island of Honshu on Friday was the strongest quake ever measured in Japan. The National Earthquake Information Center (NEIC) of the USGS in Golden, CO, determined its magnitude as 8.9. NEIC scientists routinely use recordings from seismometers from all over the world to compute the strength of a quake. The Japanese Meteorological Agency, which is responsible for earthquake monitoring and tsunami warning in Japan, determined the magnitude as 8.8. Their scientists computed the value from regional seismic networks.
Even though the magnitude of Friday's quake was very large and some coastal areas in northeastern Honshu's Miyagi prefecture were devastated, the quake was by no means the worst natural disaster to hit Japan. On September 1, 1923, large parts of Tokyo and Yokohama were destroyed by the "Great Kanto Earthquake" and subsequent fires, which raged for days. More than 100,000 people lost their lives and almost 400,000 buildings were destroyed. More than 5,500 people died on January 16, 1995 in southern Honshu when the region around Kobe was hit by a quake with a magnitude of 6.9. The damage to Kobe's infrastructure was severe, as the quake toppled elevated freeways and submerged docks in the busy harbor.
On a global scale as well, Friday's quake off the coast of northern Honshu was one of the strongest temblors ever measured with seismometers. When using the USGS magnitude of 8.9, it ranks fifth on the list of most severe quakes in the last century, topped only by the 9.5 quake in Chile in 1960, the 9.2 quake in Alaska in 1964, the 9.1 Indian Ocean quake on Boxing Day 2004, and the 9.0 quake on the Russian Kamchatka Peninsula in 1952.
The seismic waves from Friday's quake were registered all over the world. It took about 12 minutes for the first seismic waves to reach the US West Coast and be recorded by the Berkeley Digital Seismic Network here in Northern California. The seismogram shown here was captured at station BKS, which is located in a tunnel just above the University Botanical Gardens.
On the other hand, it took many hours for the tsunami to cross the Pacific. Around 8 am (PST) the first effects were measured on the West Coast. In Crescent City the Tsunami reached a height of 7 feet, and along the Monterey coast the wave was three feet high, while hardly anything could be measured in the region around the Golden Gate. There the arrival of the tsunami coincided with low tide. (hra061)