G-EVER Updates

April 26, 2022

I. Machida, M. Ono, and A. Marui

Institute for Geo-Resources and Environment

There are two major aquifers* beneath Kumamoto City and surrounding areas: the first shallower aquifer and the second deeper aquifer, the latter of which is the most important groundwater resource for the area. In the vicinity of the Lake Ezu, the base of the first (shallower) aquifer locates about 20m below sea level, and that of the second (deeper) aquifer locates about 200m below sea level (Figure 1).

Previous studies have shown that the major recharge area* of the second aquifer is the middle course of Shirakawa River (“Recharge area” in Figure 2). The distribution of hydraulic head in the second aquifer shows that the most groundwater flows southwestward from the recharge area (blue arrows in Figure 2). Since the fault whose rupture has reached the ground surface this time runs south of Kumamoto City, it is not very likely that the earthquakes generate drastic changes in the conditions of the groundwater resources in the area as a whole. However, crustal expansion or contraction and strong seismic vibration may cause temporal changes in groundwater level and turbidity. Careful observation needs to be continued.

The Figures below are included in “7. Kumamoto Area” of the Water Environmental Map series published by GSJ (2014). Original maps were published by Kumamoto City, Kumamoto Prefecture (1995).

Figure 1. Elevation of the base of the second aquifer* in meters above sea level, which substantially differs by location (GSJ, 2014). Traces of the fault lines are from Kumamoto City, Kumamoto Prefecture (1995).

Figure 2. Distribution of hydraulic head in meters in the second aquifer (GSJ, 2014). Groundwater flows orthogonally to the contour from higher level to lower.

* Aquifer: a geological layer that contains groundwater resource.

* Recharge area: a land area where surface water infiltrates into an underground aquifer

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Report 3 (April 22, 2022): Emergency Survey Report

Posted on April 22, 2022 by Shinji Takarada

Updated on April 22, 2022

The contents of this website are English translation of the Japanese website of “Report 3: Emergency Survey by Y. Shirahama, H. Mori, T Maruyama, and M. Yoshimi“,

An emergency survey was conducted near the epicenter of the 2016 Kumamoto earthquake to survey surface deformations, starting on April 16 after the M7.3 earthquake (Figure 1). Surface ruptures are identified along the northern Hinagu fault zone (Takano-Shirahata segment), and Futagawa segment and a part of Uto segment of the Futagawa fault zone (Figure 1). Surface deformation suggesting an earthquake fault is also observed in Uto area of the Futagawa fault zone. Photos of some earthquake faults and surface deformation are shown below (Photos 1 to 16).

Valuable and helpful information about the location of the earthquake faults on the ground was provided by Dr. Takashi Nakata, Emeritus Professor at Hiroshima University, Professor Hiroyuki Goto, Kyoto University, and Dr. Masashi Omata of Pasco Corporation.

Figure 1. Distribution of surface rupture and deformations identified in the current survey. The base map is the Active Fault Map in Urban Area (Ikeda et al., 2001) by the Geospatial Information Authority of Japan (modified from GSJ, 2016).

Photos of identified surface earthquake faults

Photo 1. Northeastward view of right lateral displacement producing mole-track structure in a field at Douzon, Mashiki Town. The fault line extends into a hill in the back of the photo, passing by a blue vinyl greenhouse. White arrows indicate the location of the fault line and red arrows show the sense of displacement (April 16, 2016; taken from GSJ, 2016).

Photo 2. Right lateral displacement in a field of Douzon, Mashiki Town (northwestward view). Right lateral offset of the footpath in the field is about 200 cm (April 16, 2016; taken from GSJ, 2016)

Photo 3. Shortening deformation on the paved road in Kamijin, Mashiki Town (southeastward view). The fault runs N70E with vertical displacement of about 40 cm (April 16, 2016; taken from GSJ, 2016).

Photo 4. Right lateral displacement with mole-track structure in the west of Shimojin, Mashiki Town (northeastward view). Lateral displacement is about 100 cm and vertical displacement is about 20 cm (April 16, 2016; taken from GSJ, 2016).

Photo 5. Vertical displacement of about 35 cm is observed to continue to the crossing in the back of the photo, in a field of Mitake, Mashiki Town (northeastward view; April 16, 2016; taken from GSJ, 2016).

Photo 6. The flexural deformation in a drained paddy field with N70W left lateral component, west of Shimojin, Mashiki Town (west-northwestward view). Vertical displacement is about 15-20 cm and left lateral displacement is about 20 cm (April 16, 2016; taken from GSJ, 2016).

Photo 7. Right lateral displacement in a drained paddy field, southwest of Mitake, Mashiki Town (northeastward view). The fault can be traced to the place shown in Photo 5, through a deformed guardrail, crossing the road and passing the right side of a house in the far back of the photo (April 16, 2016; taken from GSJ, 2016).

Photo 8. Right lateral displacement of about 40-50 cm in a parking lot of a community center in Akai, Mashiki Town (northwestward view; April 16, 2016; taken from GSJ, 2016).

Photo 9. Northeastward view of right lateral displacement in a drained paddy field and mole-track structure, west of Togawa, Mashiki Town. (April 16, 2016; taken from GSJ, 2016).

Photo 10. Right lateral displacement of about 50 cm in a drained paddy field, west of Togawa, Mashiki Town (south-southeastward view; April 16, 2016; taken from GSJ, 2016).

Photo 11. Vertical displacement of about 15 cm, cutting the national route 443 at the south of the Iino Elementary School (west-southwestward view; April 16, 2016; taken from GSJ, 2016).

Photo 12 Right lateral displacement on the road pavement, west of Tsuchiyama, Mashiki Town (westward view; April 16, 2016; taken from GSJ, 2016).

Photo 13. Right lateral displacement of about 50 cm in a drained paddy field at Takaki, Mifune Town (southward view; April 17, 2016; taken from GSJ, 2016).

Photo 14. Right lateral displacement shown by the offset of gutter in the southern border road of Kamitakano, Mifune Town (eastward view). The right lateral displacement indicated by the offset of the gutter is about 50 cm (April 17, 2016; taken from GSJ, 2016).

Photo 15. Open cracks with vertical offset of the road pavement along the southern border of Kushijima, Mashiki Town (east-northeastward view). The vertical offset of the road surface is about 10 cm. The sporadic distribution of open cracks from northeast to southwest in the paddy field is shown by white arrows (April 16, 2016; taken from GSJ, 2016).

Photo 16. Open cracks along the boundary between topographic high and drained paddy field, south of Kushijima, Mashiki Town. The open cracks were created on the ramp of south-side-up flexure. The fence beyond the person was deformed by the flexure (west-southwestward view). The vertical displacement of the ground along the flexure is about 20 cm or more. The south-side-up flexure and open cracks continuously distributed along the topographic boundary. Curved white arrow shows flexure ramp shape (April 17, 2016; taken from GSJ, 2016).

Reference:

Yasutaka Ikeda, Noboru Chida, Takashi Nakata, Heitaro Kaneda, Masayoshi Tajikara, Shinji Takazawa (2001) Active Faults in Urban Area Map [Kumamoto], GSI Tech. Rep. D.1-No.368.

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2016 Kumamoto Earthquake Report 2 (April 17, 2022): Seismic activities and related information in central Kyushu since April 15, 2022

Posted on April 17, 2022 by Shinji Takarada

Last updated on April 21, 2022

The contents of this website are English translation of the Japanese website of “2016 Kumamoto Earthquakes and related information“, the Geological Survey of Japan (GSJ), AIST.

Seismic activities has been increasing in Kumamoto Prefecture and Oita Prefecture, and landslides occurred in many places of the Minami-Aso Village, near the Aso volcano.

Seismic activity and geological information in central Kyushu

Orange circles denote epicenters of two major earthquakes: M6.5 earthquake at 21:26 JST on April 14 and M7.3 earthquake at 01:25 JST on April 16 determined by Hi-net of the National Research Institute for Earth Science and Disaster Prevention (NIED). Blue circles are aftershocks and other smaller earthquakes from 00:00 JST, April 14 to 07:00 JST, April 16, which were also determined by Hi-net (NIED). Size of the circles is proportional to the magnitude of the earthquakes. Red lines show traces of active faults in this area. Base map is 1:200,000 Seamless Geological Map of Japan (GSJ, AIST). (modified from GSJ, 2016)

Epicenters of the present earthquake sequence show extremely wide distribution in the zone of Beppu-Shimabara Graben from the west to the east coast of the middle Kyushu with a distance of about 200 km and a width of a few tens of km. The earthquake sequence are presently very active at Hinagu Fault Zone and Futagawa Fault Zone in western Kyushu, Aso Volcano area in central Kyushu, and Beppu-Haneyama Fault Zone in eastern Kyushu.

Distribution of epicenters plotted on 1:200,000 geological maps in Kumamoto Prefecture

The Hinagu Fault Zone and Futagawa Fault Zone, which were the sources of the M6.5 earthquake on April 14 and the M7.3 earthquake on April 16 respectively, are located between a hilly area of Cretaceous accretionary complex and Jurassic metamorphic formations in the south, and a flatter area of Kumamoto Plain and Yatsushiro Plain in the north. The M6.5 earthquake at 21:26 JST on April 14 was on Hinagu Fault Zone and the M7.3 earthquake at 01:25 JST on April 16 was on Futagawa Fault Zone.

Distribution of epicenters around the two major earthquakes in Kumamoto plotted on 1:200,000 geological mapsCircles indicate epicenters of earthquakes determined by Hi-net (NIED). Orange circles are the two major earthquakes. Size of the circles is proportional to the magnitude of the earthquakes (modified from GSJ, 2016).

1:200,000 geological maps of “Kumamoto (Hoshizumi et al.,2004)” and “Yatsushiro and a part of Nomozaki (Saito et al., 2010)” by GSJ, AIST (modified from GSJ, 2016).

Distribution of epicenters plotted on 1:200,000 geological maps around Aso Caldera.

Seismic activity has increased around Aso Caldera, Kumamoto Prefecture, after the M7.3 earthquake at 01:25 JST on April 16. The epicenters are located in the northern half of Aso Caldera and aligned along a NE-SW direction.

Blue circles are earthquakes from 00:00 JST, April 14 to 12:00 JST, April 16, determined by Hi-net (NIED). Size of the circles is proportional to the magnitude of the earthquakes (modified from GSJ, 2016).

Distribution of epicenters plotted on 1:200,000 geological maps in Beppu area

Seismic activity has also increased in Beppu City and Yufu City, Oita Prefecture, after the M7.3 earthquake at 01:25 JST on April 16. The epicenters are located along Beppu-Haneyama Fault Zone and are aligned along a ENE-WSW direction.

Landslides in Minami-Aso Village in Aso Caldera

Many landslides occurred in the Minami-Aso Village, located within the Aso Caldera, after the M7.3 earthquake on April 16. Among them, large one on the slope above the west of Aso-Ohashi Bridge on Kurokawa River broke the bridge completely. This area is located in the western caldera wall of Aso Caldera and underlain by pre-Aso Caldera lava and pyroclastic rocks erupted 80k to 40k years ago. The caldera wall is steep and can collapse by a strong earthquake motion. Other landslides, including those at the Jigoku Hot Spring, occurred on steep hills of post-caldera lava flow deposits inside the caldera.

(Taken from GSJ, 2016)

(Taken from GSJ, 2016)

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2016 Kumamoto Earthquake Report 1 (April 15, 2022): Aftershock distribution and geology in this area

Posted on April 15, 2022 by Shinji Takarada

Last updated on April 21, 2022

The contents of this website are English translation of the Japanese website of “2016 Kumamoto Earthquakes and related information“, the Geological Survey of Japan (GSJ), AIST.

An orange circle denotes the epicenter of the main shock determined by Hi-net (NIED) and blue circles stand for after shocks (until 9:00 on April 15). Red lines show traces of active faults in this area. Base map is 1:200,000 Seamless Geological Map of Japan (GSJ, AIST). (modified from GSJ, 2016)

Figures below show after shock distribution and geology in this area.

Close-up of the figure above. Symbols are the same as above. Base geological map is 1:200,000 Kumamoto (Hoshizumi et al.,2004) and Yatsushiro and a part of Nomozaki (Saito et al., 2010) by GSJ, AIST (modified from GSJ, 2016).

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Influence of the Kumamoto Earthquake on groundwater resources

The M6.5 and M7.3 Kumamoto Earthquakes on April 14 and 16, 2016

Posted on April 15, 2022 by Shinji Takarada

Last updated on May 17, 2022

The contents of this website are English translation of the Japanese website of “2016 Kumamoto Earthquakes and related information“, the Geological Survey of Japan (GSJ), AIST.

A moderate earthquake of M6.5 occurred in Kumamoto Prefecture, Kyushu, southwestern Japan, at 21:26 JST on April 14, 2016. It was generated on a right-lateral strike-slip fault, northern part of the Hinagu fault zone. Depth of the epicenter was shallow (about 11 km in depth; JMA), and very strong ground motion was recorded near the source fault. A larger earthquake of M7.3 occurred at 1:25 JST on April 16, 2022 on the Futagawa fault zone, which is the northern neighbor of the Hinagu fault zone.

The Geological Survey of Japan (GSJ) set up the Emergency Survey Headquarters on April 15 to conduct systematic responses.

Report 3 (April 22, 2022): Emergency Survey Report

Report 2 (April 17, 2022): Seismic activities and related information in central Kyushu since April 15, 2022

Report 1 (April 15, 2022): Aftershock distribution and geology in this area

Related websites

Update information

May 17, 2016: Influence of the Kumamoto Earthquake on groundwater resources is released.
April 22, 2016: 2016 Kumamoto Earthquake Report 3 is released.
April 17, 2016: 2016 Kumamoto Earthquake Report 2 is released.
April 15, 2016: 2016 Kumamoto Earthquake Report 1 is released.

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