Hi Petra. You know me. I have got to stir the pot up once in awhile. If I don’t I get bored. Of course there are times when I do this I whined shooting myself in the foot.

What you say about those who believe that earthquakes can be predicted is true. For the most part they have gone quietly about their job gathering data here and there and putting it together.

Parkfield is one such place where data is being gathered. Yea I know. You and I have butted heads on this in the past, and probably will continue to do so in the future. While it’s true that Parkfield has not yielded the data they are looking for which of course is the 22 year 6.0Ml+ quake they have never the less learned that there are precursors to large events.

The key problem is simple: a lack of data. The right kind of data that is. There are so many variables; it's hard to put it together.

All this seismic activity around semi famous Parkfield occurs along a stretch of the infamous San Andreas Fault, a segment that at times is the source of big earthquakes, and at other times just slowly and quietly creeps along. At the surface, researchers use creepmeters to measure how much the ground moves, over time, around the fault (and you thought it was keeping an eye on the neighbors...). But until recently, nobody has had a clear picture of extent of movement below the surface, down there where the bulk of the big problems originate.

Figuring that out involved studying not the big earthquakes that Parkfield prides itself on, but by looking at 6,000 tiny temblors that have struck in relative obscurity around the equally tiny town since 1987. These microearthquakes, as they're called, are less than magnitude 1 and wouldn't be noticed even by the most seasoned Parkfielder.

To measure these microearthquakes, researchers dug a bunch of boreholes 820 feet into the ground. Then they dropped in some seismometers, devices that measure the movement of the ground. Robert Nadeau and Thomas McEvilly, both of the Lawrence Berkeley National Laboratory, then began to study a flurry of data over a number of years.

Here's what's important: Nadeau and McEvilly found relationships between the microearthquake activity, the slip rate, and larger earthquakes. Moderate quakes of magnitude 4.2 to 5.0 occurred within a few months to two years after the underground slip rate increased. If you are a seismologist, this is a pretty big deal.

Here are some of the things that have been found to occur before some large earthquakes.

Foreshocks -- small shocks that sometimes occur before a big one

Changes in groundwater chemistry

Pressure of fluids in underground rocks

Creep -- slow movement along faults

Earthquakes in adjacent parts of a fault

Statistical analysis of earthquake frequency

Changes in local magnetic field

Strain in underground rocks

A large earthquake cannot take place without there being sufficient deformation to yield the energy released by the earthquake. Although details of the time and place of the earthquake itself may be unpredictable, a number of recent studies confirm that analyzing seismic shear waves along appropriate ray paths can monitor the build-up of deformation before a large earthquake. Monitoring the build-up of deformation (which we shall call earthquake forecasting) is a much simpler and better understood phenomenon than earthquake prediction. This is demonstrated by a comprehensive range of evidence including observations before earthquakes, laboratory experiments in stress cells, and a comprehensive numerical (APE) modeling procedure, which all demonstrate that forecasting earthquakes is possible. Forecasting is used in the sense of recognizing the build-up of stress before earthquakes, analogous to the use of air pressure to forecast the weather.

Rockmass Deformation
The key to monitoring deformation and earthquake forecasting is the new understanding of the microscale deformation of rocks. Almost all rocks contain distributions of fluid-filled intergranular microcracks and intergranular pores (EDA-cracks). The fluid is usually water, and these water-filled "voids" are the most compliant elements of the rockmass. If the rock is squeezed in any way, water migrates along pressure-gradients between neighboring intergranular microcracks at different orientations to the stress field so that some cracks become fatter and some thinner. This makes the rock effectively anisotropic to seismic shear-waves and causes the shear-wave splitting observed in almost all rocks. Your ear tones show that. You and others like you are hearing what they are trying to see.

The ability to predict earthquakes is here. The money needed to accomplish it isn’t. Take Care…Yea old pot stirrer Don in creepy town.