Field survey Report: Earthquake damage survey in Nagano, Japan

At 10.08 PM on 22 November 2014, the earthquake struck the middle part of Honshu Island, Japan. The Japan Meteorological Agency reported it was magnitude 6.8 while the U.S. Geological Survey (USGS) reported it was magnitude 6.2. The mechanism of this earthquake found to be the Thrust type or reverse fault earthquake. The exact local time of the occurrence was on 2014-11-22 22:08:18PM. The epicenter was located in the northern part of Nagano prefecture at Latitude 36.7N, Longitude 137.9E with the hypocenter depth of 12 km.

Figure: PGA (Source NIED)

Peak ground acceleration distribution is provided by K-NET and KiK NET can be seen in Fig. It shows that near the epicenter the peak ground acceleration found around 500 gal to 200 gal. Also, the peak ground acceleration obtained from each observed station. The maximum PGA of about 570.0 gal can be observed at station NGN005 which is about 4 km from the epicenter and the second largest is at NGN002 with 385.0 gal which is about 30 km from epicenter. Ground motions in these two stations are plotted in Fig. with Fourier spectra and response spectra. Response spectra calculated in this report considered single degree of freedom of structure.

Since 1941, there are 6 earthquakes have struck this region. Most of the past earthquakes recorded within this region, are in range of 6.1- 6.9 Magnitude earthquake. Most recent earthquake before the latest one on 22 November 2014 was that shook this area in 2011 with Magnitude of 6.7 and it occurred only one day after the 2011 Tohoku earthquake.

Fig: History of Eq near Nagano (http://mainichi.jp/select/news/20141123k0000m040090000c.html).

The Japan Meteorological Agency seismic intensity scale is a seismic scale used in Japan. This scale is normally used to measure the intensity of earthquakes. It is measured in units of shindo, seismic intensity, lit. "degree of shaking"). Unlike the moment magnitude scale which measures the energy released by the earthquake, the JMA scale describes the degree of shaking at a point on the Earth's surface.  The summary of tables explaining JMA seismic intensity scale is shown in Fig.

According to the JMA seismic intensity scale,　The highest intensity scale observed near the epicenter mostly within the range of 6 lower to 5 lower whereas those which located further the scale becomes lower which is about 3 to 1. For the some area in Nagano prefecture that experience the strong shaking the JMA seismic intensity scale found to be 6- in Nagano city, Otari village, Ogawa village, 5+ in Hakuba village, Shinano town, and 5- in Itoigawa city, Myoko city, Nakano city, Omachi city, Izuna town.

Ground motion recorded in station NGN005 which is just about 4 km apart from epicenter shows there was two shocks where they have about 15 sec of time lag even for just about 30 km apart NGN002 does not recorded like two shocks that might integrated during movement of wave. Major shock of this earthquake transmitted in N-S direction with predominant period of about 0.2 to 0.5 seconds. Ground motion was amplified in station NGN002 due to its site condition that has shear wave velocity of just 170 to 225 m/sec up to 7 m depth with soil density of 1.5 g/cm³ where 255 to 295 m/sec in NGN005 with soil density about 2.2 g/cm³. A response spectrum is quite flat in peak with the range 0.2 – 0.5 sec in near site but it has dominance in 3 sec near site NGN002.

Damage survey

1.    Otari Village Office

This office is the main center for sending help and support to the damage area. In case of emergency, the officers are operated according to Emergency Action Plan. Also, all necessary groups and individuals are gathered here in this office for making a plan and sending help to the damage area. Our team arrived at the office around 13:00PM and we acquired some information about the locations of the damaged area and also the information about another local office and evacuation center.

2.    Village office and evacuation shelter, Hakuba village

After visited Otari Village Office, we have been told that in Horinouchi and Oide, Hakuba village were severely damaged. So, we decided to visit the Hakuba village office and evacuation shelter and the team arrived at the office around 14.00PM. In the Hakuba village office, we met the vice-head of the local governer and he kindly provided us some information about the earthquake and the damaged area. Also, he took the team to the evacuation shelter to observe how they manage the evacuation plan in the time of emergency and gave the team some information about the evacuee. However, it quite took long time to have a chance to talk with him due to the busy schedule he had during the time like this. So, after obtained some information, the team went to the damage area directly. 

3.    Horinouchi, Hakuba village

From the Hakuba village office to Horinouchi, Hakuba village, the distance is about 5-6 km. However, some roads were damaged following the earthquake. Therefore, the team was forced to use another road which took more time that the main road and the team could get to the damaged area at Horinouchi around 15.30 PM.

As in Fig. 21, the damaged area Horinouchi, is about 6 km away from the earthquake epicenter and the NGN005 K-NET observed station, and is 5-6 km from the Hakuba village office and evacuation center. The village was located within the mountain area and surround by mountain from 3 sides; the north, the south, and the east. The approximate area of the village is about 80,000 m². Most of the buildings in this area were built for the residential purpose. The common structural type in this area was found to be 2 stories timber frame structure.

This report briefly explain the damages of road surfaces and buildings. 

Cracks on road

In this survey, there are total 15 structures have been investigated using visual investigation. However, the detailed information on structural types, year of construction, material used and design are not able to acquire this time. As it was about one day after earthquake struck this area so it was not appropriate to ask those people who just lost their properties to get any detailed information regarding their house. According to the survey, these building can be categorized into 2 mains type as use of the building that is residential and other (Office, parking, storage, etc.).  13 building are the residential houses while the rest are for other purposes. Most buildings in this area are 2-stories timber frame structure while several reinforce concrete buildings can be found as well.

House as shown below was located in the slope area. It was the 2-stories timber frame house. The 1st story was the open area for storing purpose while 2nd floor was served as the residential. The structure was found to be completely collapse. The 2nd floor found to be piled on the entire 1st floor's debris. Most columns were laid flat on ground. Besides, the cracks and movements of ground within the surrounding area can be found. For this building, the red label which indicated the building is not safe and do not entry was given.

Collapsed Building

Visual building Damage investigation of House

Number					1
Location & coordinate					36°39'1.69"N 137°51'58.07"E
Purpose of use					Residential
Year					NA
Structural type					Timber
Number of stories					2
Class of damage					Collapse
Inspection data					Name: Team*
					Date: 24/11/2014
Damage to structural elements		Damage
Structural element		Collapse			Heavy	Severe		Light
Vertical structures		ü
Horizontal structures					ü
Stairs
Roofs						ü
Wall and partitions		ü
Damage to Non-structural elements		Damage
		Heavy			severe		light
Falling of covering, ceiling		ü
Falling of internal or external objects					ü
Damage to hydraulic or sewage plant		ü
Damage to electronic or gas plant		ü
Soil and foundation		Damage(length, width)
		Heavy			severe		light
Settlement					ü
Slope failure
crack		ü
Liquefaction
Failure of the foundation structure
Inspection Accuracy	üFrom outside		Partial	complete		Not inspected

This report was prepared by team of Earthquake and Lifeline Engineering Laboratory, Kyoto University, Japan. You can find the full report here in this link.