It is widely known that earthquakes can trigger disastrous landslides but, what about the opposite? Can landslides trigger earthquakes?
Earthquakes are triggering factors that can activate slope instabilities known as co-seismic landslides. Those slides are caused by inertial forces and may vary in size and shape. Usually, the ground failure is quick and sudden, a fact that makes co-seismic landslides hazardous for human civilization. The impact of an earthquake in a given slope is dependent on the energy that arrives at the site which is mainly controlled by the magnitude of the quake, the epicentral distance, the topography amplification and the stratigraphy.
A new research endeavor conducted by scientists in the GFZ German Research Centre for Geosciences and other colleagues, comes to answer the opposite question. The study was published in Scientific Reports.
The research was driven by a series of earthquakes that struck Taiwan 11 years ago. "In 2009, typhoon Morakot delivered ~ 3 m of precipitation in southern Taiwan, causing exceptional landsliding and erosion," the study reports.
Those earthquakes occurred after heavy rainfalls hit the island triggering numerous landslides. Scientists estimate that 1.2 km3 soil and rock material was displaced as a result of around 100,000 landslides. This amount is equivalent to 4,800,000 Olympic size swimming pools.
Taiwan is a region that experiences earthquakes, however, by analyzing 20 years of data and 340,000 seismic shocks that occurred in the region, scientists found that the areas affected by the aforementioned landslides were impacted by far more earthquakes than normal. The seismic activity was recorded instantly after the rainfalls and landslides struck and persisted for about 2.5 years.
Researchers interpret this response as a result of the soil and rock mass removal that caused a slight upward displacement to the Earth's crust locally. Inferentially, there were stress alterations within the crust, a fact that may have caused faults to rupture, triggering earthquakes. "These observations suggest that the progressive removal of landslide debris by rivers from southern Taiwan has acted to increase the crustal stress rate to the extent that earthquake activity was demonstrably affected," the study mentions.
The authors of the study point out that it's not the landslides (the sudden movement of the ground downwards), that trigger those earthquakes but the redistribution of the material through the area which leads to the internal stresses' changes. For this reason, it is better to characterize these phenomena as erosion-induced earthquakes.
The knowledge of these geologic processes is currently limited since similar events are relatively rare and have not been widely documented. Nevertheless, the team suggests that future research potential is high since erosion-induced earthquakes will occur more frequently as a result of extreme weather phenomena caused by climate change.
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