A question about "the movement of fluids in the crust." What fluids are being referred to here? It is hard to gauge from the article being linked above. It is fluid contained in the original porous rock layers (water or saline)? Is it fluid from the Aegean Sea getting into the rock layers from all the faulting? Does this also include magma, being as it is also a fluid? It is all of the above? Just a bit confusing on the reference to "fluids in the crust".
If someone could give a brief explanation, that would be great. Thanks
That's a great question! While magma is a fluid (and can cause earthquake swarms), it doesn't fall under this particular umbrella.
In general, we're talking mostly about water, although there may also be CO2; these likely contain dissolved elements (salts, silica, etc.).
There are various possible sources for these fluids. Probably the most likely is fluids released from rocks at depth as they undergo metamorphism. One possibility is that fluids are being generally released across rock bodies as they are exposed to high temperatures and pressures, migrating up until they reach faults, and then traveling along them.
In some cases, there can also be meteoric water systems - i.e., systems where water circulates from the surface to depth. However, it is unclear how deeply these systems can penetrate, and in general the increasing pressures with depth tend to push fluids up towards the surface. Some studies have shown meteoric water penetration down to ~10 km, which overlaps with the hypocenters of some (but not all) of the earthquakes in this swarm. But since many of the earthquakes are occurring at 10-20 km depth, this seems relatively unlikely.
And then let's not forget the subduction system. Subducting slabs carry fluid-rich rocks and sediment into the mantle (in pore spaces, and hydrated minerals). These are then released at depth (and are actually responsible for the formation of volcanoes, like Santorini, since water changes the melting temperature of rock). At the location of the swarm, the slab is ~120 km deep, so it would be quite a travel path up to the 5-20 km depth range where the earthquakes are happening.
Hi, is a potential major earthquake here and subsequent tsunami also a threat to the nearby coastline of Turkey? What about other regions of the Eastern Mediterranean?
First, I want to be clear that the most likely scenario is that this swarm does not trigger a large earthquake.
Regarding what such an earthquake would look like, we can get some sense from the earthquake in 1956. That earthquake probably represents something like the largest possible earthquake on this fault system. You can find a map of approximate shaking intensities here: https://earthquake.usgs.gov/earthquakes/eventpage/iscgem888445/shakemap/intensity.
Note that this is a very coarse map - it doesn't take into account the NE-SW strike of the fault - but it gives a first-order sense. Given the fault orientation, I expect that the real intensity distribution was more elliptical, with the long axis oriented NE-SW.
Regarding the tsunami, Leclerc et al. (2024) show a map of tsunami run-ups in 1956. It's in their Figure 1 - the blue bars. You can see that the run-ups are pretty localized, with the highest values on the southeastern coast of Amorgos. https://www.nature.com/articles/s43247-024-01839-0
So, if a large earthquake were triggered in the region of the swarm, It would certainly be felt strongly on the western coast of Turkey, with some potential for building damage, but not severe. A tsunami is also possible, but not as high as for the more proximal islands.
For people living on the coast in earthquake-prone areas, it is always good to treat earthquakes as natural tsunami warnings -- i.e. to evacuate following shaking, and only return once there is official guidance that the coastline is safe.
1. I’ve not seen it mentioned so is there no data available to determine if any of these events express a harmonic nature that could indicate emplacement of a dike, or possibly (remote possibility) resupply of magma to the known vents along this complex fault structure? Santorini isn’t the only vent as I understand the geology.
2. Any hypothesis being offered regarding a pluton emplacement? I haven’t read sufficiently to be able to remember if batholiths are figurative in this region’s complex tectonic setting.
I'm curious to know whether the "advisories" mentioned in the report are according to a formal emergency management plan (operational earthquake forecasting plan) for anomalous seismic activity or simply a set of reasonable though unplanned measures (e.g. school closures, warnings to avoid vulnerable structures, etc.). In any case, another well written report.
Hi James, I there is a recently developed Greek earthquake response contingency plan called Enceladus, but I believe that it involves coordinated response to earthquakes that have already occurred. I do not know what if any formal OEF plans there are for a situation like this one. I haven't seen any statements from officials or researchers that make specific probabilistic claims in this case. I suspect that the recommendations are not based on a specific formal plan, but rather from long experience in Greece on the likely effects a larger earthquake would have, combined with the unusual nature of this swarm. Thanks for the comment!
Thanks Kyle: I've written to a colleague who may know about whether or not there are formal OEF plans. Will you and Judith be attending the SSA meetings in Baltimore in April?
Thank you so much for the great report. Do the quakes in this swarm being spread out point to movement where they’re bouncing around the subduction slab? (Thus looking like possible foreshocks of a major subduction rupture?)
Hi Nancy, this swarm is very shallow in the crust, between about 5-15 kilometers deep. The subducting slab is probably 80-100 kilometers deep in the same area. At those depths, a plate interface is generally too hot to generate large earthquakes - the contact can slide and smear freely rather than sticking frictionally. A large subduction earthquake along the Hellenic Trench is possible (although that is debated to some degree), but there is no reason why this swarm would be linked to one.
A question about "the movement of fluids in the crust." What fluids are being referred to here? It is hard to gauge from the article being linked above. It is fluid contained in the original porous rock layers (water or saline)? Is it fluid from the Aegean Sea getting into the rock layers from all the faulting? Does this also include magma, being as it is also a fluid? It is all of the above? Just a bit confusing on the reference to "fluids in the crust".
If someone could give a brief explanation, that would be great. Thanks
That's a great question! While magma is a fluid (and can cause earthquake swarms), it doesn't fall under this particular umbrella.
In general, we're talking mostly about water, although there may also be CO2; these likely contain dissolved elements (salts, silica, etc.).
There are various possible sources for these fluids. Probably the most likely is fluids released from rocks at depth as they undergo metamorphism. One possibility is that fluids are being generally released across rock bodies as they are exposed to high temperatures and pressures, migrating up until they reach faults, and then traveling along them.
In some cases, there can also be meteoric water systems - i.e., systems where water circulates from the surface to depth. However, it is unclear how deeply these systems can penetrate, and in general the increasing pressures with depth tend to push fluids up towards the surface. Some studies have shown meteoric water penetration down to ~10 km, which overlaps with the hypocenters of some (but not all) of the earthquakes in this swarm. But since many of the earthquakes are occurring at 10-20 km depth, this seems relatively unlikely.
And then let's not forget the subduction system. Subducting slabs carry fluid-rich rocks and sediment into the mantle (in pore spaces, and hydrated minerals). These are then released at depth (and are actually responsible for the formation of volcanoes, like Santorini, since water changes the melting temperature of rock). At the location of the swarm, the slab is ~120 km deep, so it would be quite a travel path up to the 5-20 km depth range where the earthquakes are happening.
Hi, is a potential major earthquake here and subsequent tsunami also a threat to the nearby coastline of Turkey? What about other regions of the Eastern Mediterranean?
Hi Alistair,
First, I want to be clear that the most likely scenario is that this swarm does not trigger a large earthquake.
Regarding what such an earthquake would look like, we can get some sense from the earthquake in 1956. That earthquake probably represents something like the largest possible earthquake on this fault system. You can find a map of approximate shaking intensities here: https://earthquake.usgs.gov/earthquakes/eventpage/iscgem888445/shakemap/intensity.
Note that this is a very coarse map - it doesn't take into account the NE-SW strike of the fault - but it gives a first-order sense. Given the fault orientation, I expect that the real intensity distribution was more elliptical, with the long axis oriented NE-SW.
Regarding the tsunami, Leclerc et al. (2024) show a map of tsunami run-ups in 1956. It's in their Figure 1 - the blue bars. You can see that the run-ups are pretty localized, with the highest values on the southeastern coast of Amorgos. https://www.nature.com/articles/s43247-024-01839-0
So, if a large earthquake were triggered in the region of the swarm, It would certainly be felt strongly on the western coast of Turkey, with some potential for building damage, but not severe. A tsunami is also possible, but not as high as for the more proximal islands.
For people living on the coast in earthquake-prone areas, it is always good to treat earthquakes as natural tsunami warnings -- i.e. to evacuate following shaking, and only return once there is official guidance that the coastline is safe.
I hope this helps!
-Judith
Thanks! That is reassuring.
Two related questions:
1. I’ve not seen it mentioned so is there no data available to determine if any of these events express a harmonic nature that could indicate emplacement of a dike, or possibly (remote possibility) resupply of magma to the known vents along this complex fault structure? Santorini isn’t the only vent as I understand the geology.
2. Any hypothesis being offered regarding a pluton emplacement? I haven’t read sufficiently to be able to remember if batholiths are figurative in this region’s complex tectonic setting.
I'm curious to know whether the "advisories" mentioned in the report are according to a formal emergency management plan (operational earthquake forecasting plan) for anomalous seismic activity or simply a set of reasonable though unplanned measures (e.g. school closures, warnings to avoid vulnerable structures, etc.). In any case, another well written report.
Hi James, I there is a recently developed Greek earthquake response contingency plan called Enceladus, but I believe that it involves coordinated response to earthquakes that have already occurred. I do not know what if any formal OEF plans there are for a situation like this one. I haven't seen any statements from officials or researchers that make specific probabilistic claims in this case. I suspect that the recommendations are not based on a specific formal plan, but rather from long experience in Greece on the likely effects a larger earthquake would have, combined with the unusual nature of this swarm. Thanks for the comment!
Thanks Kyle: I've written to a colleague who may know about whether or not there are formal OEF plans. Will you and Judith be attending the SSA meetings in Baltimore in April?
I'm afraid we can't make it this year. But please do let us know what you find out!
Thank you so much for the great report. Do the quakes in this swarm being spread out point to movement where they’re bouncing around the subduction slab? (Thus looking like possible foreshocks of a major subduction rupture?)
Hi Nancy, this swarm is very shallow in the crust, between about 5-15 kilometers deep. The subducting slab is probably 80-100 kilometers deep in the same area. At those depths, a plate interface is generally too hot to generate large earthquakes - the contact can slide and smear freely rather than sticking frictionally. A large subduction earthquake along the Hellenic Trench is possible (although that is debated to some degree), but there is no reason why this swarm would be linked to one.