GPS Data Could Detect Large Earthquakes Hours Before They Happen

Subject :Geography

Section: Physical geography

Context:

A systematic global analysis of GPS time-series data from nearly 100 large earthquakes suggests the existence of a precursory phase of fault slip that occurs about two hours before seismic rupture.
Though predicting large earthquakes is still challenging.

The Challenge of Short-term Earthquake Prediction:

Short-term earthquake prediction, which involves issuing a warning anywhere from minutes to months before a quake, depends on the presence of a clear and observable geophysical precursor signal.
Prior retrospective studies have proposed that a slow aseismic slip can be seen in faults ahead of the main shock, serving as a possible precursor.
However, the connection between these observations and seismic ruptures remains unclear.
This uncertainty arises as these observations do not directly precede an event and often occur without an ensuing earthquake, leaving the existence of a precise precursory signal for predicting large earthquakes in question.

Significance and Limitations of the Study:

These findings suggest that many large earthquakes initiate with a precursory phase of slip, or the observations may represent the concluding part of a longer and more challenging to measure process of precursory slip.
The current earthquake monitoring instruments lack the necessary coverage and precision to detect or monitor for precursory slip at the scale of individual earthquakes.
It is not clear whether such slow-slip accelerations are distinctly associated with large earthquakes or whether they could ever be measured for individual events with the accuracy needed to provide a useful warning.

What are faults?

Faults are fractures in Earth’s crust where rocks on either side of the crack have slid past each other.
Sometimes the cracks are tiny, as thin as hair, with barely noticeable movement between the rock layers. But faults can also be hundreds of miles long, such as the San Andreas Fault in California and the Anatolian Fault in Turkey, both of which are visible from space.
There are three kinds of faults: strike-slip, normal and thrust (reverse) faults.
Each type is the outcome of different forces pushing or pulling on the crust, causing rocks to slide up, down or past each other.Each describes a different kind of relative motion.

Types:

Strike-slip faults indicate rocks are sliding past each other horizontally, with little to no vertical movement. Both the San Andreas and Anatolian Faults are strike-slip.
Normal faults create space. Two blocks of crust pull apart, stretching the crust into a valley. The Basin and Range Province in North America and the East African Rift Zone are two well-known regions where normal faults are spreading apart Earth’s crust.
Reverse faults, also called thrust faults, slide one block of crust on top of another. These faults are commonly found in collisions zones, where tectonic plates push up mountain ranges such as the Himalayas and the Rocky Mountains.

Difference among these faults:

Strike-slip faults are usually vertical, while normal and reverse faults are often at an angle to the surface of the Earth. The different styles of faulting can also combine in a single event, with one fault moving in both a vertical and strike-slip motion during an earthquake.