59 Recent Advances in Geomorphology, from the Mountains to the Coast (Posters)

Sunday, 25 September 2016
9:00 AM - 5:30 PM
Exhibit Hall E/F

EARTHFLOW DEPOSITS TRIGGERED BY THE 2016 KUMAMOTO EARTHQUAKE IN ASO CALDERA, SW JAPAN

Paper number: 59-6
Program: Technical Sessions
Time: 9:00 AM – 5:30 PM

Authors

Abstract

The 2016 Kumamoto earthquake is a series of earthquakes that includes a Mw 7.0 main shock that struck at 01:25 JST on April 16, 2016 beneath Kumamoto City in Kyushu Island, SW Japan, at a depth of about 10 km. One of the foreshock earthquakes had a Mw 6.2 at 21:26 JST on April 14, 2016 and occurred at a depth of about 11 km. The two earthquakes killed at least 49 people and injured about 3000 others in total.

The main shock triggered more than 100 collapses of loam deposits that cover the post-caldera volcanoes of Aso caldera. The loam deposits contain soil, weathered ash and noticeable tephra layers such as the Aso-Kusasenrigahama pumice (30 cal kBP) and the Aira Tn ash (29 cal kBP). This is the first report of the occurrence and distribution of earthflow deposits. A geomorphological map of the Takanohane volcano area shows that earthflow deposits can be categorized into a few units, we infer these units represent sector collapses that occurred multiple times during the shaking.

Nearby, related earthflow deposits flowed relatively long distances down and along the San’oudanigawa River. At Ko-eboshi volcano, slope collapse occurred over a wide area. A large number of loam blocks from slope rushed down valley to the volcano’s foot and were able to travel long distances without water saturation. These traveling and depositional modes are similar to the effects of a debris avalanche.

Geological Society of America Abstracts with Programs. Vol. 48, No. 7

doi: 10.1130/abs/2016AM-280500

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.