Follow-up to "A Bunch of Small Tremors in Bluffdale"
Here's a follow-up to http://fulnessoftimes.blogspot.com/2017/06/a-bunch-of-small-tremors-in-bluffdale.html. I was going to just add it as an update to that post, but figured it's been more than a few days and it should probably just be a new post.
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A second tremor on June 28 in the Bluffdale area, this one only a magnitude 1.1. Two small ones, a 0.5 and a 0.8, on July 1. And a 1.6 on July 2.
A 30 day history of the area shows 26 tremors since June 20, nothing prior to that date.
The history since June 5, 2010, shows 28 tremors in the area, with the oldest two happening in November 2016. Going back to the year 2000 shows the same 28.
I did the same search back to the year 1900.
And got the same results, only 28 earthquakes in the area.
I triple-checked the search to make sure I was getting it right. As a side note, I don't think the USGS had much in the way of sensors for the smaller quakes in Utah prior to the early 1970's. My reasoning is there wasn't anything earlier than that decade, and I fairly certain there would have been something recorded.
A similar search, but expanded to cover the area from Farmington down to American Fork, and from the mountains to the west end (tailings ponds) of the Salt Lake valley resulted in 148 quakes, with the oldest being a 2.2 in March 1978.
Remember, the Bluffdale area has only had reported quakes since November 2016 and there have been 28, most of which occurred since June 20, 2017.
Using those numbers, almost 19% of the reported earthquakes of magnitude 0.5 or larger have happened in the Bluffdale area since November 2016. Or, 17.5% of the 148 quakes have been since June 20, 2017.
I know those are low magnitude quakes. The highest of the 148 was a 4.5 in 1983 and a 4.4 in 1992. There were a few in the 3-range.
However, I still think it might be significant and it would be good to watch this area. And, I really think the pressure is getting transferred to another area on the fault segment. I still don't think a larger quake is about to happen in our immediate (next few months) future, but it's always a possibility.
My feeling on this is there will probably be a number of additional quakes, not large enough to really call much attention or to make people think something bigger is about to happen. Maybe not even as frequent as have been happening, but if they do I will think my hypothesis is probably right.
Most likely small tremors will continue until right before a large quake strikes the fault segment. While not indicative of when or how big an future earthquake will be, I suspect that the more of these which happen will result in a larger earthquake in the future on a different part of the fault segment. Here's my thought. Maybe the Salt Lake segment would be about to have a 5-range earthquake, but when that happens it actually would be two or more places along the fault which slip at nearly the same time, but only the highest single point on the fault actually registers as the epicenter. However, by having another section (or more) of the fault having some pre-slipping, it causes more pressure to build on what will eventually be the epicenter, most likely the place where the pressure is greatest (too bad we can determine where that area is).
Here's an overly simplistic scenario that is kind of what I'm referring to. You could think of multiple pillars holding up a weight. The weight isn't spread evenly across the entire bottom, but the pressure of the weight is distributed among all the pillars. A single pillar breaking results in more pressure/weight being transferred to the other pillars. With a single pillar breaking there may be a little movement detected, but it would be insignificant. Losing several more pillars, each individually, over a period of time would slowly transfer more and more pressure/weight to fewer pillars. Eventually the weight is being supported by only a few, and when a key pillar breaks it results in a lot of pressure crashing down.
Obviously, a fault isn't holding up a weight, although the fault is an area of pressure between two crust plates. But the fault-line is not smooth, nor is it even, as the was the overly simple pillar-weight example. There are most likely areas with greater pressure and places with less pressure because the plates are not pressing evenly across the entire fault due to the fact that the fault is not the same along it's full length. There are different materials, different "edges," and other differences along the length of the fault, as well as its depth. Each of these will affect how much pressure the fault can hold before giving way by slipping or thrusting.
Additionally, how other (distant) crustal plates are pushing and transferring pressure might also affect how the local crustal plates are pressing against each other. This could then also affect how the local pressure points are affected.
So, my thought is if the segment were to have a 5-range earthquake on one part, with at least one other area of the fault slipping in conjunction with it, then if those other areas release enough pressure before a large quake happens, it might cause the main area to increase in its pressure and the coming earthquake would be in the 6-range. Similarly, if enough pressure gets transferred from smaller quakes in other areas, then the resulting large quake might be in the 7-range. I'm not saying this is the case in all fault zones, but it does make sense that it could be the case in some large earthquakes.
Along these lines, a slightly larger quake on the main pressure points, without the release of much pressure at the minor points, would cause the pressure to shift to those other, lesser points. With the remaining fault pressure now being spread over a more points, the larger quake would likely result in a delay of a future big quake. Of course the problem still remains that we don't know where areas of low or higher pressure might be along a fault, although I'm guessing the experts might be able to make a reasonable calculation.
---update July 5, PM---
Add two more to the Bluffdale total, a 0.9 [update 7/6/17 AM--I believe this was revised to a 0.8, sometimes it takes a day or two for a magnitude to be settled on] and 1.0 for today (so far). That makes 30 since last November, with 28 in the last two weeks. Really makes me wonder what's going on. I know mine explosions can cause minor earthquake reports, but the USGS usually identifies these quakes as being the result of a mine explosion, or other factor (such as volcanic activity).
These types of earthquake "swarms" are similar to those that make people concerned when they happen at a volcano (Mt. Saint Helens has had similar swarms over the last couple decades, with no eruption), or at Yellowstone. But those places tend to have somewhat regular occurrences of swarms, for example, Yellowstone usually has an uptick in the late spring, early summer, which results in lots of warnings that Yellowstone is about to blow. But, it hasn't happened, yet.
Another item of interest is there appears to be a clustering of small quakes in the Park City area. The earliest reported was a 3.4 in 1995, so there probably wasn't much in the way of monitoring before then. There was a 3.5 in 1999, a 2.8 in 2005, and a 2.5 in 2009. Four quakes from 0.7 to 1.8 in 2013. 2014 saw 13 quakes ranging from 0.5 to 1.8. There were only 3 in 2015, 2.3, 0., and 0.8. 2016 also saw three quakes; 1.6, 1.2, and 0.8.
So far, 2017 has had 12 quakes in the area. The earliest 2017 quake was on June 28, a measly 0.6. But the remaining quakes have all happened since July 2. The lowest was 0.5 and the highest was a 2.3.
For 2017, so far, 11 quakes in the Park City area and 28 in the Bluffdale area. Clusters on either side of the Salt Lake segment of the Wasatch Fault (although Park City is further away from the fault than Bluffdale). I can't find any fault zone maps for either area, so my guess is they are related to the SL segment.
---update 7/6/2017 9:16 AM---
Two more Bluffdale quakes to tally up. Both were last night about 10:05 PM (UTC time was 04:05 July 6), and another at 10:34 PM. They were 1.6 and 1.7. That brings the total to 32 since last November when the tremors started.
I was wondering if somehow, maybe, there was some heavy construction going on which might be contributing to the mild tremors, but I'm not aware of anything that big, or which would be happening during the night hours or weekends (when several of the quakes have occurred).
Something is definitely going on. Based on the past 40+ years of quake history in the area, this is very unusual for the area.
---update 7/14/2017
Just checked the last seven days, because I hadn't noticed any seismic activity being reported when I've checked on most days over the last week. I have noticed it sometimes takes a bit of time for the USGS to get things posted and/or updated. And sometimes I may just be checking right after the 24 hour mark since a quake, so I miss it being reported.
Three more quakes on July 8th, and two on the 11th, all in the 1.0 to 1.3 range. Total is now at 37 since November. I'm expecting at least in the 60's.
It is making me very curious as to why these small quakes are happening, not that we will ever know.
--update 8/14/2017
I haven't noticed any more quakes in the Bluffdale area for a few weeks. While they were not as frequent as an earthquake swarm might be in other places, because of the rarity of the event it might possibly be considered a swarm event. It will be interesting to see where the first big Utah earthquake strikes.
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A second tremor on June 28 in the Bluffdale area, this one only a magnitude 1.1. Two small ones, a 0.5 and a 0.8, on July 1. And a 1.6 on July 2.
A 30 day history of the area shows 26 tremors since June 20, nothing prior to that date.
The history since June 5, 2010, shows 28 tremors in the area, with the oldest two happening in November 2016. Going back to the year 2000 shows the same 28.
I did the same search back to the year 1900.
And got the same results, only 28 earthquakes in the area.
I triple-checked the search to make sure I was getting it right. As a side note, I don't think the USGS had much in the way of sensors for the smaller quakes in Utah prior to the early 1970's. My reasoning is there wasn't anything earlier than that decade, and I fairly certain there would have been something recorded.
A similar search, but expanded to cover the area from Farmington down to American Fork, and from the mountains to the west end (tailings ponds) of the Salt Lake valley resulted in 148 quakes, with the oldest being a 2.2 in March 1978.
Remember, the Bluffdale area has only had reported quakes since November 2016 and there have been 28, most of which occurred since June 20, 2017.
Using those numbers, almost 19% of the reported earthquakes of magnitude 0.5 or larger have happened in the Bluffdale area since November 2016. Or, 17.5% of the 148 quakes have been since June 20, 2017.
I know those are low magnitude quakes. The highest of the 148 was a 4.5 in 1983 and a 4.4 in 1992. There were a few in the 3-range.
However, I still think it might be significant and it would be good to watch this area. And, I really think the pressure is getting transferred to another area on the fault segment. I still don't think a larger quake is about to happen in our immediate (next few months) future, but it's always a possibility.
My feeling on this is there will probably be a number of additional quakes, not large enough to really call much attention or to make people think something bigger is about to happen. Maybe not even as frequent as have been happening, but if they do I will think my hypothesis is probably right.
Most likely small tremors will continue until right before a large quake strikes the fault segment. While not indicative of when or how big an future earthquake will be, I suspect that the more of these which happen will result in a larger earthquake in the future on a different part of the fault segment. Here's my thought. Maybe the Salt Lake segment would be about to have a 5-range earthquake, but when that happens it actually would be two or more places along the fault which slip at nearly the same time, but only the highest single point on the fault actually registers as the epicenter. However, by having another section (or more) of the fault having some pre-slipping, it causes more pressure to build on what will eventually be the epicenter, most likely the place where the pressure is greatest (too bad we can determine where that area is).
Here's an overly simplistic scenario that is kind of what I'm referring to. You could think of multiple pillars holding up a weight. The weight isn't spread evenly across the entire bottom, but the pressure of the weight is distributed among all the pillars. A single pillar breaking results in more pressure/weight being transferred to the other pillars. With a single pillar breaking there may be a little movement detected, but it would be insignificant. Losing several more pillars, each individually, over a period of time would slowly transfer more and more pressure/weight to fewer pillars. Eventually the weight is being supported by only a few, and when a key pillar breaks it results in a lot of pressure crashing down.
Obviously, a fault isn't holding up a weight, although the fault is an area of pressure between two crust plates. But the fault-line is not smooth, nor is it even, as the was the overly simple pillar-weight example. There are most likely areas with greater pressure and places with less pressure because the plates are not pressing evenly across the entire fault due to the fact that the fault is not the same along it's full length. There are different materials, different "edges," and other differences along the length of the fault, as well as its depth. Each of these will affect how much pressure the fault can hold before giving way by slipping or thrusting.
Additionally, how other (distant) crustal plates are pushing and transferring pressure might also affect how the local crustal plates are pressing against each other. This could then also affect how the local pressure points are affected.
So, my thought is if the segment were to have a 5-range earthquake on one part, with at least one other area of the fault slipping in conjunction with it, then if those other areas release enough pressure before a large quake happens, it might cause the main area to increase in its pressure and the coming earthquake would be in the 6-range. Similarly, if enough pressure gets transferred from smaller quakes in other areas, then the resulting large quake might be in the 7-range. I'm not saying this is the case in all fault zones, but it does make sense that it could be the case in some large earthquakes.
Along these lines, a slightly larger quake on the main pressure points, without the release of much pressure at the minor points, would cause the pressure to shift to those other, lesser points. With the remaining fault pressure now being spread over a more points, the larger quake would likely result in a delay of a future big quake. Of course the problem still remains that we don't know where areas of low or higher pressure might be along a fault, although I'm guessing the experts might be able to make a reasonable calculation.
---update July 5, PM---
Add two more to the Bluffdale total, a 0.9 [update 7/6/17 AM--I believe this was revised to a 0.8, sometimes it takes a day or two for a magnitude to be settled on] and 1.0 for today (so far). That makes 30 since last November, with 28 in the last two weeks. Really makes me wonder what's going on. I know mine explosions can cause minor earthquake reports, but the USGS usually identifies these quakes as being the result of a mine explosion, or other factor (such as volcanic activity).
These types of earthquake "swarms" are similar to those that make people concerned when they happen at a volcano (Mt. Saint Helens has had similar swarms over the last couple decades, with no eruption), or at Yellowstone. But those places tend to have somewhat regular occurrences of swarms, for example, Yellowstone usually has an uptick in the late spring, early summer, which results in lots of warnings that Yellowstone is about to blow. But, it hasn't happened, yet.
Another item of interest is there appears to be a clustering of small quakes in the Park City area. The earliest reported was a 3.4 in 1995, so there probably wasn't much in the way of monitoring before then. There was a 3.5 in 1999, a 2.8 in 2005, and a 2.5 in 2009. Four quakes from 0.7 to 1.8 in 2013. 2014 saw 13 quakes ranging from 0.5 to 1.8. There were only 3 in 2015, 2.3, 0., and 0.8. 2016 also saw three quakes; 1.6, 1.2, and 0.8.
So far, 2017 has had 12 quakes in the area. The earliest 2017 quake was on June 28, a measly 0.6. But the remaining quakes have all happened since July 2. The lowest was 0.5 and the highest was a 2.3.
For 2017, so far, 11 quakes in the Park City area and 28 in the Bluffdale area. Clusters on either side of the Salt Lake segment of the Wasatch Fault (although Park City is further away from the fault than Bluffdale). I can't find any fault zone maps for either area, so my guess is they are related to the SL segment.
---update 7/6/2017 9:16 AM---
Two more Bluffdale quakes to tally up. Both were last night about 10:05 PM (UTC time was 04:05 July 6), and another at 10:34 PM. They were 1.6 and 1.7. That brings the total to 32 since last November when the tremors started.
I was wondering if somehow, maybe, there was some heavy construction going on which might be contributing to the mild tremors, but I'm not aware of anything that big, or which would be happening during the night hours or weekends (when several of the quakes have occurred).
Something is definitely going on. Based on the past 40+ years of quake history in the area, this is very unusual for the area.
---update 7/14/2017
Just checked the last seven days, because I hadn't noticed any seismic activity being reported when I've checked on most days over the last week. I have noticed it sometimes takes a bit of time for the USGS to get things posted and/or updated. And sometimes I may just be checking right after the 24 hour mark since a quake, so I miss it being reported.
Three more quakes on July 8th, and two on the 11th, all in the 1.0 to 1.3 range. Total is now at 37 since November. I'm expecting at least in the 60's.
It is making me very curious as to why these small quakes are happening, not that we will ever know.
--update 8/14/2017
I haven't noticed any more quakes in the Bluffdale area for a few weeks. While they were not as frequent as an earthquake swarm might be in other places, because of the rarity of the event it might possibly be considered a swarm event. It will be interesting to see where the first big Utah earthquake strikes.
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