As we known, there are many mechanisms for the triggering of landslides. How to build the relationship between a special landslide and the certain mechanism?
For a example, the South China Sea provides a set of preconditions for forming submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. And the triggering mechanism include the earthquakes, storms, currents and so on.
In my opinion, we will distinguish the preconditions and triggering mechanisms. Then, the triggering mechanism can be analyzed.
In the western ghats situated in southern India, the hill chain is made up of pre-Cambrian hard rocks. Every year landslides occur in this mountain chain during monsoon season. This hilly region is characterised by extreme slopes and weathered & fractured rocks, which are favourable for occurrence of landslides. It is established without any doubt that the landslides in this region is triggered by heavy rains (rainfall intensity). Very rarely the landslides are triggered by mild earth tremers (not earthquakes as such) in this region. Beginning of every monsoon season the District Administration alerts the people to move out of the already delineated landslide prone areas and try to provide them with safe shelters.
It is important to know that the landslides are not only triggered due to natural causes, but also due to human activities. In many places it is triggered due to human activities, especially in areas where unscientific developments are carried out in these geologically fragile zones.
Dear Dawei,
The fundamental reason for landslide is losing shear strength. Water in the soils can definitely reduce the shear strength. There are some soils which can take up more water and still have adequate shear strength compared to weaker soil that can fail immediately when water is added. Please refer to "Unsaturated soils" by Fredlund et al (2012). There are vulnerable soils such as collapsible soils, residual soils and expansive soils. The residual soils can take up more suction and will high strength with low level of water content. But, rainfall or flood event happens, this residual soils can quickly loose shear strength and thereby cause landslides. If the vulnerable areas in the deep sea and shores are identified by geophysical methods, then planning can be done to avoid these areas or minimise the risks of landslides.
Best regards
Ravi
Recent and paleo submarine landslides are widely distributed within strata of the deepwater areas along the continental slopes, uplifts and carbonate platforms on the north continental slope of the South China Sea. High resolution 3D seismic data and multi-beam data help us to identify the submarine landslides based on the seismic-sedimentology and geomorphology.
Being one of the largest sinks for fluvial sediments among enclosed or semi-enclosed marginal seas worldwide, the South China Sea provides a set of preconditions for forming submarine landslides including rapid sediment accumulation, formation of gas hydrates and fluid overpressure. We want to build the relationship between the submarine landslides and tectonic events, such as the slip reversal of Red River Fault ~5.5 Ma, Baiyun Moving ~5.5 Ma and so on.
A direct relationship between submarine landslides and tectonic events is difficult to establish because of the long-period scale character of tectonic events, even if we have seismic and drilling well data crossing the submarine landslides. We can only try to tie submarine landslide to the paleo-tectonic events by geophysical and geochemical evidence.
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