Typhoon changed earthquake patterns
Intensive erosion influenced seismicity

Date:
July 2, 2020
Source:
GFZ GeoForschungsZentrum Potsdam, Helmholtz Centre
Summary:
Intensive erosion can temporarily change the earthquake activity
(seismicity) of a region significantly.



FULL STORY ==========================================================================
The Earth's crust is under constant stress. Every now and then this
stress is discharged in heavy earthquakes, mostly caused by the
slow movement of Earth's crustal plates. There is, however, another
influencing factor that has received little attention so far: intensive
erosion can temporarily change the earthquake activity (seismicity) of a
region significantly. This has now been shown for Taiwan by researchers
from the GFZ German Research Centre for Geosciences in cooperation with international colleagues. They report on this in the journal Scientific Reports.


==========================================================================
The island in the western Pacific Ocean is anyway one of the most
tectonically active regions in the world, as the Philippine Sea Plate
collides with the edge of the Asian continent. 11 years ago, Typhoon
Morakot reached the coast of Taiwan. This tropical cyclone is considered
the one of the worst in Taiwan's recorded history.

Within only three days in August 2009, three thousand litres of rain
fell per square metre. As a comparison, Berlin and Brandenburg receive
an average of around 550 liters per square meter in one year. The water
masses caused catastrophic flooding and widespread landsliding. More
than 600 people died and the immediate economic damage amounted to the equivalent of around 3 billion euros.

The international team led by Philippe Steer of the University of
Rennes, France, evaluated the earthquakes following this erosion event statistically.

They showed that there were significantly more small-magnitude and shallow earthquakes during the 2.5 years after typhoon Morakot than before, and
that this change occurred only in the area showing extensive erosion. GFZ researcher and senior author Niels Hovius says: "We explain this change
in seismicity by an increase in crustal stresses at shallow depth, less
than 15 kilometres, in conjunction with surface erosion." The numerous landslides have moved enormous loads, rivers transported the material from
the devastated regions. "The progressive removal of these loads changes
the state of the stress in the upper part of the Earth's crust to such an extent that there are more earthquakes on thrust faults," explains Hovius.

So-called active mountain ranges, such as those found in Taiwan,
are characterized by "thrust faults" in the underground, where one
unit of rocks moves up and over another unit. The rock breaks when
the stress becomes too great. Usually it is the continuous pressure
of the moving and interlocking crustal plates that causes faults to
move. The resulting earthquakes in turn often cause landslides and
massively increased erosion. The work of the GFZ researchers and their colleagues now shows for the first time that the reverse is also possible: massive erosion influences seismicity -- and does so in a geological
instant. Niels Hovius: "Surface processes and tectonics are connected in
the blink of an eye." The researcher continues: "Earthquakes are among
the most dangerous and destructive natural hazards. Better understanding earthquake triggering by tectonics and by external processes is crucial
for a more realistic assessment of earthquake hazards, especially in
densely populated regions."

========================================================================== Story Source: Materials provided by GFZ_GeoForschungsZentrum_Potsdam,_Helmholtz_Centre. Note: Content may
be edited for style and length.


========================================================================== Journal Reference:
1. Philippe Steer, Louise Jeandet, Nadaya Cubas, Odin Marc, Patrick
Meunier,
Martine Simoes, Rodolphe Cattin, J. Bruce H. Shyu, Maxime
Mouyen, Wen- Tzong Liang, Thomas Theunissen, Shou-Hao
Chiang, Niels Hovius. Earthquake statistics changed by
typhoon-driven erosion. Scientific Reports, 2020; 10 (1) DOI:
10.1038/s41598-020-67865-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200702113658.htm

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