The 2011 Magnitude 9.0 Great Tohoku Earthquake (Northeast Honshu, Japan)

The “2011 Tohoku Earthquake” in this hub is a simplification of the official name “The 2011 off the PacificCoast of Tohoku Earthquake” by Japan Meteorological Agency. The western world often refers this earthquake as “Near the East Coast of Honshu, Japan”. The magnitude 9.0 Tohoku Earthquake of March 11, 2011 resulted from thrust faulting on or near the subduction zone plate boundary between the Pacific and North America plates, where the Pacific plate moves approximately westwards with respect to the North America plate at a rate of 83 mm/year (about 3¼ inch/year). The rupture originated about 24.4 km (15.2 miles) below the surface. The rupture was bilateral, which spread away from the epicenter in both the north and south directions, taking about 2 minutes to cover a total of 400 km (250 miles).

The epicenter is at distances of 130 km (80 miles) east of Sendai, 178 km (110 miles) east of Yamagata and east-north-east of Fukushima, and 373 km (231 miles) north-east of Tokyo. The earthquake was preceded by a series of large foreshocks over the previous two days, beginning on March 9th with a magnitude 7.3 event approximately 40 km from the epicenter of Tohoku Earthquake, and continuing with another three earthquakes greater than magnitude 6.0 on the same day. A series of more than 125 aftershocks of magnitude up to 7.9 struck an area about 150 km (90 miles) off the northeastern coast, about 440 km (270 miles) northeast of Tokyo. They struck at depths between 8 and 10 km (5 and 6 miles). Refer to Google Maps below for more information on the earthquake epicenter and the devastated area.

The magnitude 9.0 Tohoku Earthquake was more than 500 times stronger than the recent 2010 Haiti Earthquake of magnitude 7.0. The sea floor was thrust up and seaward, creating a devastating tsunami that hit the coast of Honshu within tens of minutes and propagated across the whole Pacific where a tsunami warning was issued, hitting Hawaii and the coast of California in about 4 hours and 10 hours, respectively. The earthquake followed by the tsunami mainly affected more than 2,100 km (1,300 miles) of the eastern coastline along Miyagi, Fukushima, Ibaraki, and Iwate Prefectures. The height of observed tsunami was above 7 m (23 ft) in Soma in Fukushima Prefecture and above 4.2 m (14 ft) in Oarai in Ibaraki Prefecture that washed far inland over fields, smashing towns, airports and highways in its way. The 2011 Tohoku Earthquake (M 9.0) is considered to be fourth world-wide largest earthquake according to the United States Geological Survey (USGS) after Chile Earthquake of 05/22/1960 (M 9.5), Prince William Sound Earthquake, Alaska, of 03/28/1964 (M 9.2), and Off the West Coast of Northern Sumatra Earthquake, Indonesia, of 12/26/2004 (M 9.1). All these earthquakes were followed by devastating tsunamis. Check below the tsunami waves as they reached Kesennuma Port as well as an interesting tsunami simulation video from the United States’ National Oceanic and Atmospheric Administration (NOAA).

The March 11, 2011 earthquake was an infrequent catastrophe. Historically, large offshore earthquakes have occurred in the same subduction zone in 869, 1611, 1896 and 1933 that produced devastating tsunami waves on Japan’s Pacific northeastern coast. That coastline is particularly vulnerable to tsunami waves because it has many deep coastal embayments that amplify tsunami waves. In 869, the Sendai area was swept by a large tsunami following the Jogan Sanriku Earthquake that Japanese scientists have identified from written records and research on tsunami deposits from this area. The M 7.6 subduction earthquake of 1896 created tsunami waves as high as 38 m (125 ft) and a reported death toll of 22,000. The M 8.6 earthquake of March 2, 1933 generated tsunami waves as high as 29 m (95 ft) and caused more than 3,000 fatalities. Since 1973, this subduction zone has hosted nine events of magnitude 7.0 or greater. The largest of these are: 1) An M 7.8 earthquake in December 1994 approximately 260 km to the north of the March 11 epicenter that caused 3 fatalities and almost 700 injuries, and 2) An M 7.7 earthquake in June 1978 about 35 km to the southwest of the March 11 epicenter that caused 22 fatalities and over 400 injuries.

According to the Earthquake Research Institute of the University of Tokyo; the strong ground motion due to the earthquake reached Oshika Peninsula after 35 sec, Sendai after 75 sec, Iwaki after 125 sec, and then propagated throughout the whole region of northeastern Japan in the next 70 sec. The shake reached Nagoya (in Honshu, south east of Tokyo) and Sapporo (in Hokkaido, Japan’s main island in the north) after 150 sec. Strong ground acceleration records were observed in Miyagi, Iwate, Fukushima, and Ibaraki Prefectures where a huge fault slip have occurred on the east of these areas. Preliminary research results on the slip amplitude measured on the fault surface, defined as the relative displacement of formerly adjacent points on opposite sides of the fault, was as large as 30 meters (100 feet).

Damage to buildings and infrastructure is related more closely to ground motion, rather than the magnitude of the earthquake. The peak ground displacement (PGD) was more than 100 cm (40 in) in the Sendai area, and above 50 cm (20 in) from Tohoku to the Kanto areas. The maximum recorded acceleration was over 2933 cm/sec/sec in Tsukidate observation station in Miyagi prefecture near the hypocenter. This peak ground acceleration (PGA) is almost 3.0g where “g” is the acceleration due to gravity (980 cm/sec/sec). PGA is a good index to seismic hazard of low-rise buildings and is used along with other parameters in building codes and design hazard risks.

The USGS is continuously updating the United States’ seismic hazards maps including the anticipated peak accelerations of future earthquakes on the base rock, as shown on the map below. In the vicinity of the seismic source on more detailed maps, peak rock accelerations may reach up to 2.0g in Los Angeles, 1.3g in San Francisco, 1.0g elsewhere in California, 1.0g in Washington State, 1.2g in the New Madrid area in southeastern Missouri, and 1.2g in the Charleston area in South Carolina. The peak rock accelerations are then amplified due to local soil effects by coefficient, per structural design codes, that is anywhere between 1.2 for very dense soil and soft rock conditions to 2.5 or even more for very soft clay soil conditions. The anticipated PGA is the product of the peak rock acceleration and the soil coefficient.

The Tohoku Earthquake is the most powerful on record ever to hit Japan and probably the most costly earthquake, but not the deadliest. Japan's worst earthquake in modern times was a magnitude 7.9 in 1923 in the Kanto area that that killed 142,800 people and generated a tsunami with wave heights up to 12 m (39 ft). The 6.9 magnitude Kobe Earthquake in the Kansai area in 1995 killed about 5,500 people and damaged or destroyed over 200,000 buildings and numerous bridges, and did more than $130 billion in damage. At the time, it was considered the most expensive natural disaster ever, and came as a big surprise for seismology experts because there was no evidence of large earthquakes in the Kansai area in modern times. Fortunately, my family and I survived Kobe Earthquake when I was studying “Earthquake Engineering”!

Actually, Japan has been expecting a large earthquake in the Tokai area (the central region including Tokyo and Yokohama to Nagoya). Bridges, multi-story buildings, and infrastructure have been retrofitted in this region for the next “Tokai Earthquake” according to the latest knowledge of earthquake demands and research in earthquake-resistance design. However, traditional Japanese family houses and other older buildings will have some sort of damage under moderate-to-large earthquakes. The devastated Tohoku coastal region is far less developed than the Kansai region or the Tokai area. It is largely an agricultural region and plays a smaller role in Japan’s total economic output (about 8 percent) or global trade than the port city of Kobe. Kobe port is the second largest in Japan and the sixth largest in the world, which handles 12% of worldwide Japanese exports and 31% of imports to the United States. Therefore, the economic damage is expected to remain contained to Japan, the world's third-largest economy. On 21 March, the World Bank estimated damage between $122 billion and $235 billion. Japan's government said the cost of the earthquake and tsunami in the devastated area could reach $309 billion, making it the world's most expensive natural disaster on record.

The 2011 Tohoku Earthquake is a wake-up call for people living in an area of seismic activity to prepare! How can you prepare and manage the potential costs of future earthquakes?

Earthquake Information: First, you need to investigate if you live near active fault lines. For example, California Earthquakes are expected to be generated mainly from San Andreas Fault or Hayward Fault, while the New Madrid Fault System is the major earthquake source in the Midwestern States. The USGS is publishing updated research results on earthquake prediction in California and the Midwest. The USGS website also has detailed earthquake info by state and by country/region.

Effects of Earthquakes: Earthquakes is associated with back- and forth- ground shaking which is the main reason for earthquake damage to buildings. Other earthquake hazards that may affect your home safety include liquefaction, landslide, surface fault rupture, fires, and tsunamis for major earthquakes that displace the ocean floor.

Earthquake Damage: Structural failures occur if homes are not effectively bolted to the foundation, the cripple walls are not braced, or the existence of a soft story in houses with large openings at the first level (e.g. garage doors or windows) without effective bracing. Structural damage is also influenced by building materials, year built, and number of stories. Understanding the potential earthquake damage would help you decide on seismic retrofitting.

Seismic Retrofitting: These are measures to ensure the structural integrity of your home to withstand earthquakes with little structural damage. It is necessary to seismic retrofit your home if you live within 15-25 miles from active fault lines or within regions highly susceptible to liquefaction. If you live within 25-50 miles from active fault lines and your home is constructed before the 1980’s, you probably need to retrofit it. Seismic retrofitting may be addressed one step at a time in this sequence: 1) Upgrading and adding anchor bolts to unsecured home foundations, 2) Bracing the cripple walls using structural grade plywood panels, 3) Bracing the walls of the soft story using steel members, and 4) Anchoring the connections of walls and masonry chimney to the floors and roof.

Risk Mitigation of Home Contents: Those earthquake mitigation measures are simple techniques to secure the contents of your home (e.g. tall and heavy furniture, fragile and expensive objects, and water heaters) to the studs of the interior walls or floors using inexpensive hardware tools and materials found in hardware stores. Items in the garage shall also be secured to reduce damage to vehicles. Such self-mitigation techniques can be undertaken by homeowners as they are simple to explain and require no special expertise, materials or tools to implement. You should mitigate the contents of your home whether you seismic retrofit it or not.

Earthquake Insurance: Homeowners insurance does not cover earthquake damage to your home, home contents, or personal belongings, but covers other kinds of damage that may result from earthquakes, such as fire and water damage due to burst gas and water pipes. Your vehicles are only covered under the comprehensive part of your auto insurance policy. Therefore, most of the property damage caused by an earthquake will end up being paid for by you, along with other personal debt. How do you plan to protect your assets and investments from the costs of destructive earthquakes? Earthquake insurance is an option for effectively managing these potential costs.

Emergency Preparedness Plan: Emergency preparedness is to know how to setup your own disaster planning before an earthquake that may be followed by a tsunami hits your area. A disaster plan shall include: 1) Survival Kits for each household member, 2) Emergency Kit for your household, 3) Survival Food and Emergency Drinking Water for at least 2 weeks, 4) Emergency Training by taking the Red Cross first aid and cardiopulmonary resuscitation emergency training course, and participating in the annual Great California ShakeOut Drill, if you live in California, and 5) Earthquake Survival and Disaster Recovery: by knowing what to do during and after an earthquake?