A new study published in Geochemistry, Geophysics, Geosystems revealed that the slow, gradual slip movement in the depths of subduction zones between adjacent tectonic plates can be a key to understanding how the destructive thrust earthquakes that occur there.
Slow slide mechanism
Massive thrust earthquakes occur at the confluence of tectonic plates – also called subduction zones – where a tectonic plate is pushed underneath another adjacent plate. These subduction zones are particularly concentrated around the Pacific and Indian Oceans, and can lead to massive tsunamis.
And the study team from Penn State University believes in the press release on December 21 that these slow slide events do not occur in all subduction zones. But it can affect the accumulation of trapped pressure forces underground, and cause energy to be distributed in different directions in the form of destructive earthquakes that do not necessarily follow the movements of the tectonic plates themselves.
The researchers explained that the movement that is associated with the occurrence of earthquakes is in the opposite direction to the direction of movement of the plates usually, while in slow-slide events the direction of movement is directly downward with the direction of gravity rather than the directions of plate movement.
Using monitoring data from high-precision GPS stations, the team of researchers over several years analyzed slip motions along the Cascadia subduction zone (stretching from Vancouver Island in Canada to Northern California).
The subduction zone Cascadia had witnessed a great earthquake with a magnitude of 9 on the Richter scale, and since then the slow slide events continued down the subduction zone, moving for short distances and at a slow rate.
The researchers believe that despite the occurrence of these slow-sliding earthquakes many miles below the surface, their movements could affect the timing and behavior of destructive thrust earthquakes. With a frequency of up to a year or two, it can actually lead to devastating earthquakes.
These slow slide events were first discovered by geologists about 20 years ago, and only recently were GPS devices sensitive enough to capture its movements in detail, 35 kilometers underground in this condition.
The results of the new study will help the scientific community to build simulation models for future earthquakes of this type, in which some of the pressure caused by the movement of plates in subduction zones is released by slow slide events deep in the earth.
Moreover, knowing the direction of forces that future earthquakes will trigger is extremely important in planning them. Although these natural disasters are highly unpredictable, any information that can be gathered in advance is a remarkable contribution to adding new data on the physics of devastating earthquakes.