In this field survey, it became clear that from the magnitude 7.3 earthquake on April 16, surface earthquake faults were identified along part of the Futagawa fault zone and in the northern part of the Hinagu fault zone, emerging on the surface.

During the survey, a maximum of approximately two meters right-lateral strike-slip in the Futagawa fault zone was measured, while in the northern section of the Hinagu fault zone, a maximum of approximately 50 centimeter right-lateral strike-slip was recorded.

It is difficult to conduct field surveys on land in the east side of the Futagawa fault zone, since the area around the Aso Ohashi bridge has been affected by landslides and rescue work is being carried out, making it hard to actually go into the area. However, from aerial images taken by the media and other sources, we can see there is a high probability that a surface earthquake fault has appeared. Therefore, the surface earthquake fault may stretch further east than what was identified during this survey.

Furthermore, as for the surface earthquake fault of the Hinagu fault zone, we have discovered a surface earthquake fault in an area further south from what has been reported from the academic society as of now; we may be able to identify a displacement farther south, which may again, extend the surface earthquake fault even more south.

The actual direction and extent of the slippage of the earthquake fault on surface, gives us a clue in estimating how the underground moved during the earthquake. The distribution of the slippage of the fault deep underground can be recognized by analyzing seismic waves up to some degree, but material evidence can only be obtained by measuring the extent of the slippage on surface.

When an earthquake caused by an active fault, like the Kumamoto Earthquake occurs, first, as mentioned above, we begin by studying the surface earthquake fault: the location (including the spatial continuity), and the extent and pattern of the slippage (such as right-lateral strike-slip, left-lateral strike-slip, normal fault-type, or reverse fault-type, to clarify the characteristics of the active fault.

Google Earth was used in preparing this map.

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