Reply to I am a earthquake seismologist. AMA. 5th anniversary of Louisa Quake

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[quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous]Any predictions for the next year or so?  Where will be the next big one?[/quote]

There is no valid method for predicting earthquakes.  The current state of the art on earthquakes is that the source is random...the in some cases, the small earthquake will not stop for a while, and grows to be a big earthquake.  In other cases (most cases) it stops.  [/quote]

Then how do we know "big ones" are going to hit certain areas based on data and how do we know the San Andreas fault is loaded with energy and going to pop soon - we can't predict the dates/times of earthquakes but scientists absolutely can take data and determine if a quake is going to hit within a good idea. Cmon. [/quote]

We can look at historical data to say an area is more likely to have earthquakes because we know there have been past earthquakes.

In addition, plate tectonics shows us where there should be significant faults.  Add in GPS data, and we can see where the earth is deforming.  For example, the North Amarican plate is moving south relative to the pacific plate.  In California, the slip rate is several centimeters/year.  The motion concentrates on the San Andreas Fault, but includes other faults (e.g., Hayward fault, the various thrust faulting adjacent to the San Andreas Fault, the normal faulting in the Basin and Range.

Putting it all together, we can say which areas are more likely to have earthquakes.  Fast plate motions => more earthquakes.  That is Alaska.  For the probabilistic hazard analysis, we can draw maps of shaking probability.  But, outside of plate boundaries, they just show where earthquakes have occurred.

And because of this, we get surprised.  Prior to 2004, conventional wisdom was Northern Sumatra / Andaman islands was not capable of producing a large earthquake.  Then it did.

Prior to 2011, the conventional wisdom was the subduction off Sendai Japan produced a maximum earthquake of 8.3.  But, on March 11, 2011, that view changed over a few minutes with a 9.1 earthquake.

Similarly, when I was in graduate school, there was debate that the Cascadia subduction zone off the Pacific NW was Aseismic because there were no earthquakes.  Paleoseismic and paleotsunami studies, which look at geological effect to understand earthquake/tsunami history prior to written history, indicated there had been past earthquakes.  As the science has progressed, particularly with ability to model tsunamis, scientists looked at the "orphan tsunami of Jan 27-28 1700":  [url]https://pubs.er.usgs.gov/publication/pp1707[/url].
This was a tsunami recorded in Japan without a known source.  Modeling the tsunami arrival times and the tsunami and the amplitudes, they concluded that the orphan tsunami was triggered by a magnitude 9.0 earthquake in Cascadia on Jan 27, 1700.  That is how we know the Pacific Northwest is a hazard area.  The report is very easy to read, and a wonderful combination of combing through historic reports coupled as data to feed into modern computer simulations.

Anyway, that is how we know which areas are more likely to have an earthquake.[/quote]

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