As the Day of Rapture, which is allegedly upon us on Saturday, is supposed to include a terrible earthquake, we can assume the magnitude of this event must be greater than 5.0. In which case, I need to revise my prediction. If I want to play it safe, I could say two earthquakes of this magnitude will strike before the day is out. But I won't be making any money on that bet, as the average number of earthquakes of magnitude 5 or higher is four a day.
**Get alerts of major earthquakes sent to you by email from the USGS and follow along as the day progresses.**
On average the number of earthquakes that will strike each year include: 1 earthquake of magnitude 8 or larger; 17 earthquakes of magnitudes ranging from 7 to 7.9; 134 earthquakes of magnitudes ranging from 6 to 6.9; and 1,319 earthquakes of magnitudes 5 to 5.9. But lower magnitude earthquakes are more common. For example, more than a million earthquakes in the magnitude 2 to 2.9 range strike each year.
With all these earthquakes rattling the lithosphere on a regular basis, saying an earthquake is coming is about as pointless as saying the wind will blow. The questions that need answering are where, when, and how strong. But currently only risk analysis -- based on stress accumulation, historical patterns, the geology of a region, the tectonics of the region, and so forth -- is possible. Perhaps in the future atmospheric analysis will be included in estimating risk. But currently, those looking at radon levels in the ionosphere, are making bold assertions of predictive possibilities that still need better data and, importantly, peer-review to back them up.
Growing up in Southern California, the common knowledge was that an earthquake was the physical release of pressure along the fault. Aftershocks were considered the latent release of the same pressure or neighboring pressure from shifts in the fault-line as a result of the original quake. As earthquakes and their aftershocks struck, the likelihood of a bigger quake to follow was reduced - or so the thinking went. Now we know that's not always the case.
As the events in Japan recently demonstrated, even big earthquakes of magnitude 7 or 8, as has occurred historically along Japan's offshore trench for centuries, are no indication that the stress is being relieved. In addition, even a large earthquake such as the 7.3 that struck on March 9, can be a foreshock of a larger one to come. The problem is there is currently no way to tell if the original quakes are foreshocks to a larger quake or not, unless and until a larger quake manifests.
In yesterday's Science Express, geophysicists with the California Institute of Technology (Caltech) published a model of the estimated fault slip due to the 9.0 Tohoku‑Oki megathrust event. Their findings, coupled with two other reports with lead authors from the University of Tokyo and the Japan Coast Guard, are helping to identify the tectonic aspects that led to such a surprising event as well as clarifying what is beyond current knowledge. The Caltech researchers made a point of marking what is unknown in their map with a giant white question mark.
"Instead of saying a large earthquake probably wouldn't happen there, we should have said that we didn't know," said lead author Mark Simmons in a press release. The section of the fault that failed catastrophically on March 11, had remained stable while other sections around it had shifted over the years.
"The Pacific Plate and the Okhotsk Plate had been pinned together for a long time, probably 500 to 1000 years, and finally failed in this magnitude 9.0 event," explained seismologist Hiroo Kanamori also with Caltech.
Just south of the point where the Tohoku‑Oki earthquake ruptured, another area has displayed similar eerie quiet over the centuries. "The highest amounts of stress aren't found where the paper has just ripped, but rather right where the paper has not yet been torn," Simons says.
Calculating stress build-up is possible on land with GPS measurements, but underwater observations of shifts in the seafloor are still a remote and difficult operation to achieve. Early seafloor geodetic stations around Japan were first deployed in 2002.
Now it is clear that better monitoring of the seafloor will be critical in helping to obtain the information needed in terms of risk analysis. "It is important to note that we are not predicting an earthquake here," emphasizes Simons. "However, we do not have data on the area, and therefore should focus attention there, given its proximity to Tokyo."
Read more at Discovery News
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