15:30 〜 17:00
[HDS05-P02] Evolution Comparison of large earthquake-induced and extreme rainfall-induced landslide
キーワード：landslide evolution, landslide characteristic, extreme rainfall-induced landslide
The rate and location of landslide recovery after the large earthquake or extreme rainfall events play essential roles in developing the watershed management strategies for watersheds with a dense landslide. The landslide recovery in the watersheds with dense landslides after large earthquake events was related to the earthquake magnitude, geological settings, and fault distribution and characteristics, while that after extreme rainfall events were most related to the distribution of drainage network. Several researchers had discussed the changes in the distribution and activeness of landslides after extreme rainfall-induced or earthquake-induced events. The evolution characteristic of extreme rainfall-induced landslide events during 2009 Typhoon Morakot in Taiwan in the study was also compared with that of large earthquake-induced landslide events in the world, including 2005 Kashimir earthquake and 2008 Wenchuan earthquake.
The characteristic of landslide recovery after the large earthquake or extreme rainfall events are worth comparing and discussing. The time, location, and rate of landslide recovery after the large earthquake or extreme rainfall events are the key discussion topics in this study. The oscillating period can be defined as that the annual landslide area and landslide number in this period is an oscillating trend instead of a stable decline trend. The oscillating period for the serious earthquake-induced landslide events ranged from 3 to 5 y. The extreme rainfall-induced landslide events in the study were estimated as 5 y, i.e. from 2010 to 2014. The landslide in the watersheds in the oscillating period was active and easily induced, re-induced, or enlarged. The average annual landslide area decline rates (abbreviated as LAD) after 2014 were larger than that during the oscillating period (from 2010 to 2014), and the average LAD during or after the oscillating period in this study was also larger than those from the large earthquake-induced landslide events. This means that the recovery rate of the extreme rainfall-induced landslide was faster than that of large earthquake-induced landslide.
The new or enlarged landslides in the following years after the 2005 Kashimir earthquake (including the active, very active, and extremely active landslides in [5]) were mostly located along the Muzaffarabad fault or in the high fractured and jointed rocks areas, or along with the drainage network, or in the source of the river and large landslide. And the new or enlarged landslides in the following years after the 2008 Wenchuan earthquake (the active landslides in [4]) were located in deep gullies, the source of debris flow and large landslides. The new or enlarged landslide in the sub-watersheds with dense landslide after 2009 Typhoon Morakot in Taiwan also centralized along with the drainage network, particularly in the upstream watersheds. Hugh sediment yield from the landslide in the upstream watershed with dense landslide should be the main reason. Huge sediment was yielded, deposited in the narrow reaches, and dominated the evolution of landslide and river geomorphology in the northeast Ailiou river watershed and upstream Taimali river watershed.
Huge sediment in the upstream watershed was continuously transported into the gullies and rivers and also resulted in the frequent occurrence of new or enlarged landslides in the neighborhood of gullies and rivers from 2010 to 2015 in the Ailiou river watershed. 51.3%, 54.0%, and 58.2% of the landslide areas after 2009 in the Ailiou river watershed had been recovered in 2010, 2013, and 2015. The new or enlarged landslide area from 2010 to 2015 in the Ailiou river watershed showed a continuously increasing trend. The occupied percentage of a new or enlarged landslide located in the neighborhood of gullies from 2010 to 2015 was 53.9%–56.1%, and the area of a new or enlarged landslide located in the neighborhood of the river from 2010 to 2015 also showed an increasing trend.
The characteristic of landslide recovery after the large earthquake or extreme rainfall events are worth comparing and discussing. The time, location, and rate of landslide recovery after the large earthquake or extreme rainfall events are the key discussion topics in this study. The oscillating period can be defined as that the annual landslide area and landslide number in this period is an oscillating trend instead of a stable decline trend. The oscillating period for the serious earthquake-induced landslide events ranged from 3 to 5 y. The extreme rainfall-induced landslide events in the study were estimated as 5 y, i.e. from 2010 to 2014. The landslide in the watersheds in the oscillating period was active and easily induced, re-induced, or enlarged. The average annual landslide area decline rates (abbreviated as LAD) after 2014 were larger than that during the oscillating period (from 2010 to 2014), and the average LAD during or after the oscillating period in this study was also larger than those from the large earthquake-induced landslide events. This means that the recovery rate of the extreme rainfall-induced landslide was faster than that of large earthquake-induced landslide.
The new or enlarged landslides in the following years after the 2005 Kashimir earthquake (including the active, very active, and extremely active landslides in [5]) were mostly located along the Muzaffarabad fault or in the high fractured and jointed rocks areas, or along with the drainage network, or in the source of the river and large landslide. And the new or enlarged landslides in the following years after the 2008 Wenchuan earthquake (the active landslides in [4]) were located in deep gullies, the source of debris flow and large landslides. The new or enlarged landslide in the sub-watersheds with dense landslide after 2009 Typhoon Morakot in Taiwan also centralized along with the drainage network, particularly in the upstream watersheds. Hugh sediment yield from the landslide in the upstream watershed with dense landslide should be the main reason. Huge sediment was yielded, deposited in the narrow reaches, and dominated the evolution of landslide and river geomorphology in the northeast Ailiou river watershed and upstream Taimali river watershed.
Huge sediment in the upstream watershed was continuously transported into the gullies and rivers and also resulted in the frequent occurrence of new or enlarged landslides in the neighborhood of gullies and rivers from 2010 to 2015 in the Ailiou river watershed. 51.3%, 54.0%, and 58.2% of the landslide areas after 2009 in the Ailiou river watershed had been recovered in 2010, 2013, and 2015. The new or enlarged landslide area from 2010 to 2015 in the Ailiou river watershed showed a continuously increasing trend. The occupied percentage of a new or enlarged landslide located in the neighborhood of gullies from 2010 to 2015 was 53.9%–56.1%, and the area of a new or enlarged landslide located in the neighborhood of the river from 2010 to 2015 also showed an increasing trend.