Strong 6.4 earthquake strikes Kumamoto, Kyushu, Japan

by Artemis on April 14, 2016

A strong magnitude 6.4 earthquake (subsequently revised down to M6 by the USGS) has struck the Kumamoto region of Kyushu, the southern of the main islands of Japan. Some damage reports are emerging, but the impact is currently largely unknown although not expected to be too significant.

The earthquake struck at 9.26pm local time, around 7km southwest of Ueki, Japan, at a depth of 10km, resulting in strong shaking and a warning in Japan that appeared to be off its Shindo scale for earthquake intensity. For the latest updates scroll down.

Kumamoto, Japan earthquake shake map

Kumamoto, Japan earthquake shake map - From the USGS

Initial reports suggest some damage has occurred, with a government agency reporting buildings downed, and news agency NHK saying at least 10 homes were damaged and exterior walls had fallen in some areas. At least one fire has also been reported.

Given the time of the evening and the fact it is dark, the full extent of any structural damage may not become clear until tomorrow.

It appears likely that some insurance claims will emerge, but the initial reports would not suggest a reinsurance, ILS or catastrophe bond market impact. The USGS said that it does not expect significant damage from a quake such as this.

The reinsurance, ILS and cat bond markets are of course exposed to Japanese earthquake risks, but it seems likely that losses from today’s quake would come in well beneath the layers where ILS capital tends to be deployed, based on the currently available information.

We will update this article should it emerge that the damage is more significant than initially thought.


A second earthquake, officially an aftershock, has shaken the same area and caused additional damage to houses, according to reports.

The USGS has the second quake as a magnitude 6.0 (initially recorded by Japan as M6.4), while Japanese media put it as a magnitude 6.4. News sources report some people being trapped in rubble of properties damaged. This second quake was also at a depth of 10km, so caused shaking at a similar level to the first.

There have been many aftershocks in the M3 to M4 range as well and further are expected, with Japanese scientists warning of the potential for more aftershocks at magnitudes up to 6.

The Japanese Red Cross have reported admitting 45 people with injuries to their Kumamoto center. Local nuclear power plants have been checked and nothing abnormal reported.

An additional concern is local volcano Mt. Aso, but scientists have reported that no abnormal readings have been detected.

A large blaze has been reported in a town of 34,000 people named Mashiki, with firefighters trying to control it.

According to Japan’s chief cabinet secretary Yoshihide Suga, at least 19 dwellings have collapsed and hundreds of phone calls have been received by emergency services due to damage reports to buildings.

Still, as it is night time in Japan, the actual extent of the damage is unknown currently.

Risk modelling firm RMS had the following to say in an update on the Kyushu earthquake:

Kyushu, Japan Earthquake, Mj6.4 (Mw6.1)
Event Date: 14-Apr-2016
Last Modified: 14-Apr-2016
Earthquake; Asia Pacific

At 12:26 UTC today, Thursday April 14, an earthquake of magnitude Mj 6.4 on the Japanese earthquake magnitude scale (equivalent to moment magnitude Mw 6.1) struck roughly 5 mi (8 km) northwest of the city of Kumamoto (pop. ~731,000) on the island of Kyushu, Japan. Damage reports at this early stage are limited, although at least 10 buildings have collapsed in Kumamoto according to one report. A government spokesman has stated that ‘several’ buildings have collapsed. Kumamoto police have not yet determined the extent of damage or injuries. No damage has so far been reported in neighboring Miyazaki Prefecture.

Japan Rail suspended all operations on the Kyushu Shinkansen (bullet train) line following the earthquake. On the Shinkansen line connecting the mainland (Honshu) with Kyushu, power was lost between two stations but operations have now resumed. Kyushu Electric Power Co. has said that it is not found any abnormalities in its Sendai nuclear plant in Kagoshima Prefecture in southern Kyushu. Images show shelves knocked over in offices and supermarkets, and parts of the ceiling at Uki City Hall, south of Kumamoto, have reportedly collapsed. Some people are reportedly trapped under building debris.

The maximum shaking that was felt was level VIII (‘severe’) on the Modified Mercalli Intensity (MMI) scale, according to the United States Geological Survey (USGS). However, this level of shaking was only experienced by ~100 people. Approximately 917,000 people felt MMI VII (‘very strong’) shaking, including in the cities of Kumamoto-shi, Ueki, Uto and Tamana. A further 604,000 people felt MMI VI (‘strong’) shaking, including in the cities of Yamaga, Matsubase, Ozu, Omuta, Shimabara and Kikuchi. According to the USGS, the population in the region resides in structures that are resistant to earthquake shaking, though some vulnerable structures exist. There have been no reports of fatalities so far.

Earthquake Parameters.

According to the Japanese Meteorological Agency (JMA), the earthquake had a magnitude of Mj 6.4 on the Japanese earthquake magnitude scale and was relatively shallow, with a focal depth of 6.2 mi (10 km). Mj is the local magnitude defined and calculated by the JMA, and can be converted to moment magnitude (Mw) which is the scale used by the United States Geological Survey (USGS). Mj 6.4 is the equivalent to a moment magnitude Mw6.1 earthquake (Mw = 0.78*Mj+1.08). The USGS reported a slightly stronger moment magnitude, Mw6.2, but the same focal depth as the JMA, 6.2 mi (10 km).

According to the JMA, the epicenter of the earthquake was 32.7°N, 130.8°E, while the USGS reports an epicenter of 32.8°N, 130.6°E. The earthquake lasted about 30 seconds, according to several witnesses. According to the JMA, the earthquake is unlikely to cause a tsunami. The USGS has recorded at least three aftershocks following the main earthquake.

Updates 15th April:

Reports suggest at least 9 deaths from yesterday’s earthquake as well as hundreds of injuries. The Japanese government is assessing the impact, with a number of buildings collapsed and many reports and signs of of structural damage to other dwellings and buildings, as well as some fires and structural damage to roads or infrastructure, it could be a few days before any reasonably accurate estimate emerges.

The USGS gave a potential range for economic damage, with a 65% chance of losses being between $1 billion to $10 billion yesterday, simply based on the level of shaking experienced. The economic damage from 2011’s Tohoku earthquake was thought to have been around 15% insured, so based on that an economic loss of $1 billion could represent an insurance industry loss of $150m, while a $10 billion economic loss could represent a $1.5 billion insurance industry loss.

At those levels of loss much of the insurance industry impact will be retained by primary companies, including the cooperative Zenkyoren, however there would be the potential for some claims to fall on the reinsurance industry as the estimate rose towards the upper end, we’d assume.

100’s of aftershocks have hit the region since the initial quake, but nothing as significant as the two magnitude 6+ quakes which caused the majority of the damage.

Here is the latest update from risk modelling firm AIR Worldwide:

Kyushu Rocked by a Strong and Shallow Earthquake: AIR

BOSTON, April 14, 2016 – According to catastrophe modeling firm AIR Worldwide, A strong and shallow earthquake occurred on Kyushu, the most southwesterly of Japan’s four main islands, at 9:26 p.m. local time (12:26 UTC) on April 14. The temblor was centered near the town of Mashiki in Kumamoto Prefecture, about 1,300 km (800 miles) southwest of Tokyo. The Japanese government issued a high-level alert in the southern province and alerted disaster management teams. Damage to buildings and some casualties are being reported. The earthquake has been followed by a series of aftershocks, but there is no risk of a tsunami.

The United States Geological Survey (USGS) currently estimates the intensity of the initial temblor at M6.2, and the Japan Meteorological Agency (JMA) currently estimates it at M6.4. The depth has been initially estimated by the USGS as 23.3 km (14.4 miles) and by the JMA as 10 km (6.2 miles). Shaking started modestly, grew more violent, and lasted about 30 seconds.

Kumamoto Prefecture is situated in the center of Kyushu and contains 14 cities. More than 8 million people live within 100 km (62 miles) of the epicenter of this earthquake.

“Kyushu Island lies on the overriding plate above the Philippine subducting plate to the west of the Nankai subduction zone,” Dr. Mehrdad Mahdyiar, vice president at AIR Worldwide. “The region is exposed to subduction interface, intra-slab, and shallow crustal earthquakes. During the last 50 years, the region within 150 km of the present earthquake experienced about 55 M5.0 and larger earthquakes, with a few M7.0 or larger interface earthquakes. However, historically there has not been any record of large M8.0 subduction interface earthquakes in this area.”

Dr. Mahdyiar continued, “Geologically, a large right-lateral shear zone running through the central part of Kyushu divides the island. This shear zone is an extension of the Median Tectonic Line (MTL) that originates at Honshu Island and transects Shikoku Island. The MTL is the largest tectonic line in southwestern Japan. Most seismotectonic studies and data from past earthquakes in this area indicate earthquakes with right-lateral strike-slip and extensional rupture mechanisms. Kyushu Island hosts significant volcanic activity. The volcanic front runs through the central part of the island from north to south, and a group of volcanoes is also located on a line obliquely crossing the volcanic front.”

A recent detailed regional stress analysis (Matsumuto et al., 2015) using faulting mechanisms of past earthquakes indicates a principal stress distribution with the NE-SW shear zone, consistent with the right-lateral faulting behaviors and extension field with normal faulting in the central part of Kyushu, northeast of the location of the present earthquake. The extension feature is attributed to the Ryukyu Trench, located in southeastern Kyushu, rolling back and inducing regional seafloor spreading.

Damage and casualties from the area are now being reported. In Mashiki several houses have been flattened, and occupants may be trapped inside; several fires have been noted. Roads have been damaged, and at least 10 buildings have collapsed in Kumamoto City, the capital of the prefecture. Elsewhere, large cracks have been reported in several structures. Walls of some houses have collapsed in the city of Ueki, and part of a city hall ceiling fell. Gas and power outages have occurred in areas close to the epicenter.

The Sanyo Shinkansen “bullet train” service briefly lost power and has been suspended on Kyushu as a precaution. The Kyushu Electric Company reports no issues at the Genkai or Sendai nuclear power plants on Kyushu or at the shut-down Ikata plant on nearby Shikoku.

No immediate damage was reported in neighboring Miyazaki Prefecture.

According to AIR, buildings in Japan are predominantly wood, steel, or steel-reinforced concrete. Residential exposures are dominated by single-family homes, nearly of which 90% are of wood construction. Apartment complexes in Japan are usually of steel or steel-reinforced concrete construction; only about 24% are of wood construction. Among commercial buildings, wood is even rarer and is only used for about 12% of the building stock with most of them being steel or steel-reinforced concrete. The small industrial building stock is primarily of steel or light metal with about 20% made of concrete.

Older buildings in Japan are typically quite vulnerable to shake damage, as many were built under the misguided view that a higher degree of stiffness prevents building failure. As research and construction techniques have improved, building codes have been updated to increase safety.

Dr. Mahdyiar concluded, “Japan experiences around 20% of the world’s most powerful earthquakes, but its rigid building codes and their strict enforcement mean that powerful tremors frequently do little damage, at least to engineered structures. However, as initial reports of this event confirm, vulnerable structures still exist.”

The USGS issued a green alert for shaking-related fatalities, indicating a low likelihood of casualties and damage. Because some damage is possible but the impact relatively localized, a higher yellow alert level was issued for economic losses.

AIR will monitor the situation and will provide updates as warranted.

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