The fault along the south west side of Indonesia is called the Java Trench. This is a very active subduction zone where the Australian plate is being forced under the Eurasian plate. This fault system is responsible for a lot of very large earthquakes lately and there have been a lot of reports that this plate boundary is having a lot more activity lately and people have even linked it to “the end of the world.”
So I’m looking at this fault zone to see if this is true. I’m analyzing data from one end of the fault to the other and I am looking at data from USGS.gov that has detailed data from 1975 and historical data as far back as the 1800’s. By graphing and mapping the quakes for numbers per year, and numbers by magnitude I come up with some interesting numbers and trends.
One of the trends I looked at for the whole fault system was the spread of the quakes in time. Were they getting more frequent? And the answer is no. Overall there have been only more quakes after a large 7.8 or higher quake and while it might look like there are more quakes lately that is the product of the number of aftershocks from 2 quakes but after the same size quakes back in the 70’s there were just as many aftershocks as after the current set of aftershocks. And there has been no increase in large quakes either. I think that our thinking that there have been more quakes lately is more a product of reporting is better than more quakes, at least on this fault system.
One thing I have to figure out yet is if something else I noticed is just a product of reporting as well. All along the quake there are listed in the database quakes as low as 3, and I didn’t check any of the ones below 3. But if there are 3’s in the data, and there is even back to the beginning of the data set I am using, you would think all of the 3’s would be recorded, if the instruments can pick one up and record it then they should all be there, but, they aren’t.
In the Haiti fault data there are a ton of 3’s, lots of 4’s, some 5’s, a few 6’s, and 7 and up are rare. In the Java trench data it’s a bell curve with the highest number being 4.5 or 4.6 consistently. And a 3 is as rare as a 8. Now if it was just under reporting you would think that say new equipment would pick up smaller quakes so the 3’s should all be in the last year but no, there are 3’s in the early data. So if they could pick up and did include some 3’s you would think they would include them all? They do in other places, Japan, the Caribbean, Chile. I don’t know why they would not include them here and since they include some I have to assume they include them all and that makes this subuction zone just weird.
Also in the data I looked for any increase in activity to foreshadow any major quakes and nothing. Doing all the analysis I can, and I’ve run linear regression, transform analysis, statistical analysis’ etc the only pattern that comes out is that after a major earthquake there are aftershocks.
SO what have we learned? For one, there is no increase in activity on this fault zone, it is just moving on as it has for a long time occasionally throwing up a big quake to shake things up. There is nothing in particular that happens to reliably predict a quake here, no clustering or quake storm unlike some nearby fault zones. And it may be the weirdest fault out there with more magnitude 4.X quakes than 3’s but this may be a product of someone just not recording the 3’s. (but they recorded some of them so why would they not record them all?)
- What led up to the Haiti Quake and what happens next? (echlinm.wordpress.com)