Shulou(Shulou.com)11/24 Report--

Earthquake is a natural phenomenon, which is caused by the accumulation and release of stress in the interior of the earth. When an earthquake occurs, faults in the earth's crust will suddenly slip, producing huge energy, which spreads around in the form of seismic waves, causing the ground to shake. The intensity and destructive force of an earthquake depend on the distance and speed of the fault slip, as well as the size and shape of the fault plane.

We all hope to be able to predict earthquakes so as to reduce the loss of people and property. However, earthquake prediction is a very difficult task because we cannot directly observe what is happening underground. We can only find the signals that may be related to earthquakes through some indirect methods, such as monitoring surface deformation, underground fluid pressure, electromagnetic fields, microearthquakes and so on. However, these signals are not always reliable and obvious, and sometimes they may be accidental or related to other factors. Therefore, we need to find a more effective and universal method to identify earthquake precursors.

In a recent paper published in the journal Science, the authors propose a new method to detect slow slips on faults before large earthquakes (magnitude greater than 7). Slow slip refers to a silent displacement process that occurs on a fault, which does not produce strong seismic waves, but can lead to stress redistribution in the surrounding rocks. The author believes that slow sliding may be a necessary condition before a large earthquake occurs, and it can be used as an early warning signal.

The authors used Global Positioning system (GPS) data to analyze the displacements on faults within 48 hours before nearly 90 large earthquakes. GPS can use satellites to measure the position and motion of the earth's surface. It can provide high-precision and high-frequency data. The authors selected 3026 high-speed GPS observation stations around the world and projected their displacements measured in different directions to the directions parallel or perpendicular to the fault. Then, the author adds these projected displacements and compares them with the displacement direction on the fault when each earthquake occurs.

The authors found that about 70% (63) of the 90 large earthquakes showed an obvious increasing trend in the direction parallel to the fault within two hours before the earthquake, while there was no significant change in the displacement perpendicular to the fault. These trends are in the form of exponential growth, indicating that the fault has slipped slowly and accelerated over time. These slow slips usually occur near (within 100 km) or far away (more than 300 km) from the epicenter of the earthquake and last for a short time (from a few minutes to dozens of minutes). The authors believe that these slow slips may be the sliding process (called nuclear cracking process) that occurred in a smaller area of the fault (called the core area) at the beginning of a large earthquake, or the influence of the sliding process outside the core area on the core area.

The author's research provides us with a new method to find the precursory signals of large earthquakes, which can be realized by using the existing GPS network. If we can improve the accuracy and density of GPS data, or combined with other observation methods, we may be able to detect and monitor slow slips on faults more effectively, thus warning of large earthquakes a few minutes to hours in advance. It is of great significance to reduce the disasters and losses caused by earthquakes.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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