Link established between rock stress in fault lines and earthquakes

Jul 10, 2008 10:21 GMT  ·  By

It will still take a long time before man will be able to predict an earthquake and its force, and science seems to be taking baby steps in this field, albeit when it comes to earthquake predictions any step is a big step. US researchers have recently brought new insight into the dynamics of earthquakes after detecting changes induced by stress in rocks, several hours before two small earthquakes with the epicenter in the San Andreas Fault, California, US.

"If you had 10 hours warning, from a practical point of view, you could evacuate populations, you could certainly get people out of buildings, you could get the fire department ready. Hurricane warnings give you an idea of what could be done," said Paul Silver of the Carnegie Institution for Science, part of the research team detailing the new study.

The data was collected from the San Andreas Fault Observatory at Depth located in the town of Parkfield, halfway along the fault line running across the whole state of California. This particular area experiences regular small earthquakes as the Pacific and American tectonic plates push against each other. The so-called Safod project involved the drilling of two holes, a pilot hole and a main hole containing a seismometer and a piezoelectric sensor respectively, destined to time the seismic waves propagate through the crust.

"What we're looking for are changes in the velocity that would correspond to changes in stress, and it has been hypothesised that such stress changes would precede seismic events and could be used as precursors. For a long time, people have been trying to do this. I think right now the technology has gotten better so we can measure this change more accurately," said Dr Silver.

The measurements indicated significant variations in the propagation speed of seismic waves through the crust before two earthquakes that occurred 2 and 10 hours later respectively, suggesting a possible relation between stress in the rock and an imminent tremor.

"We are very encouraged by these pre-seismic signals and are planning a series of experiments to expand on them, so that we may further understand their timing and physical basis. What happened in China was that a lot of children were killed in school in their class; so if we can predict earthquakes even by a few minutes, we can help then to evacuate the classroom," said Fenglin Niu of Rice University, leader of the research team, while referring to the China earthquake that occurred nearly two months ago.