I took a look at seismic activity in Haiti, the Dominican Republic and Puerto Rico area. This area has, at first look an a map, a lot of small earthquakes and could be a cluster. But a cluster would have a lot of earthquakes in one place then move, but it doesn’t move and it’s spread out a bit much.
So I started looking at history. When I look at 5 Magnitude and higher quakes back as
far as 1975 there are no large numbers in any one year. But when I start looking at magnitude 4 and higher (and then 3 and higher) and got a whopping 1463 (If i included 3’s I got 10,000 ) and the pattern is intriguing, there are some quakes 36 years ago, but there is a trend.
4 and higher quakes are increasing and the increase while not exactly the same each year is a linear trend. But when you add in the 3’s the trend is different, it’s still going up but it’s not linear it’s logarithmic. (2011 data not complete.)
I can hear someone somewhere saying, well there should be more, technology improvements would make it that we can see more and better, blah, blah blah. I counter this with the increases in technology allow us to see more smaller quakes further away and in other places where new technology is introduced it results in a stepped graph the numbers are constant then jump up and are constant again. But not in this data, it’s not a stepped increase but a linear at 4 and higher but an accelerated curve in the 3+ data. 5’s have stayed constant. And look at 2010, the year of the great quake in Haiti, there were actually a lot less quakes then the year before, only 500 compared to the 1200 in 2009. And 2010 is the only year there were any significant numbers of quakes at the western end (Haiti) of the zone we are looking at. Haiti doesn’t get a lot of quakes (only 185 in the period studied) and most of them have been aftershocks from the Jan 2010 Haiti quake.
All of this activity seems to have been a buildup of pressure on the fault that was released from one part of it constantly in small but increasingly frequent quakes and when the pressure built to breaking a major quake happened on the next section over and stuck part of the fault. While not a quake storm it shows a lot of the features of a quake storm making me wonder that now that the Haiti portion of that fault has let go, where is the pressure building now?
Well this fault has a lot of activity to the eastern end. These small but frequent quakes relieve the stress there and it seems that while stress builds it clears away this pressure efficiently passing it to the western end of the fault. The next portion of the quake at Haiti has let go hopefully relieving the pressure there so we have to look further west. This puts us into the Jamaica and Cuba and out to the Cayman Islands, although I expect something closer to the east end of this range before the west end.
The fault here is actually a fault zone with major faults running parallel east to west with one fault north of the other, approximately one along the Cuba shore and the other hugging the north Jamaica shore. The Cuba fault has a small number of evenly spread quakes while the Jamaica fault has few sporadic faults and it is the extension of the fault that ruptured at Haiti. The Jamaica/Cuba section of the fault had 232 quakes in the time that the Puerto Rico/Dominica section had 10 thousand.
I expect that things will quiet down a bit at the east end of the zone, only 500+ last year and only 115 so far this year, so 1998 levels, then build again in a few years. This is a fault system to watch.