Farallon??? Is this Schrödinger's cat that has already disappeared but is somehow still visible in this picture? Infinite cattiness?
PS "Small clusters of very small earthquakes at about 30 kilometers depth are also commonly seen in volcanic arcs, and probably relate to the deep plumbing system of the volcanoes. No news there." Tell me more. What is your reference for this?
Hi Simon! In the future (a week or two), Farallon (and Scotia) will have disappeared because we returned them to the local SPCA for adoption - oceanic plates are actually a pretty great analog for foster kittens in that way.
Regarding your PS, Kyle has added a response to your question at the end of the post, with a figure of part of Japan showing events in the JMA catalog below volcanoes, at ~20-40 km - presumably associated with magma plumbing systems. We don't have a reference for this, though; if you run into one, please send it our way!
Once again Earthquake Insights shows the power of scientific communication without the filter of a 6-12 month delay bandpass imposed by publication in the modern scientific literature. Judith and Kyle are to be complimented once again on their thought-stimulating writing!
Using eQuakes to scan the Global CMT dataset, one can see many candidate structures that admit to the hypothesis that the subducting slab is tearing, on deeply biting ~N-S to ~NNW-SSE faults and/or shear zones, with right-lateral sense of movement in a direction not too different from the slab dip. There is one movement picture that makes such a pattern self-explanatory, and that is if the rate of south-directed rollback increases westward, with jumps in the rate of retreat accommodated by these newly forming slab tears. Naturally, such tears propagate ruptures upwards into the overlying crustal material, and are vitally important in hindering the lateral growth of the rupture extent of the different megathrust events that occur from time to time.
Interesting, in the hinge regions, such differential movement will result in compressive stress parallel to the arc, and the deviatoric stress axes in the shear zones facilitating the tearing process will be oriented with sigma1 plunging west, and sigma3 plunging NW. In this case ductile failure (governed by the maximum moment yield condition) predicts right-lateral strike-slip faults that deep moderately steep eastward.
Most major strike-slip faults (such as the Anatolian system) are controlled by deep structures, with surficial faults spinning as they propagate upward. This is as to be expected as they adjust to the Coulomb-Mohr Yield Condition that applies to more surficial levels.
Bottom line, thanks for drawing my attention to this.
This discussion is important to trying to understand similar, but infrequent large events that have historically (since seismographs were first installed in the NW) under south central Puget Sound where the subducting Juan de Fuca plate is being forced to twist by advancing North America. In 1939, 1949, 1965, and 2001 there have been Benioff events that have cumulatively killed and hurt people and done billions of dollars of damage. Notably in Seattle the Alaska Way Viaduct was torn down and replaced with a tunnel. The 1949 event was m=>7.0, making it especially dangerous. Understanding this activity becomes more approachable when examined in the context of the Alaska, Kamchatka, and Japan tectonic settings. It’s now 24 years since the last Benioff event and it can be safely asserted that probability of another in the near to very near future is increasing. Get ready to harvest data!!!
Farallon??? Is this Schrödinger's cat that has already disappeared but is somehow still visible in this picture? Infinite cattiness?
PS "Small clusters of very small earthquakes at about 30 kilometers depth are also commonly seen in volcanic arcs, and probably relate to the deep plumbing system of the volcanoes. No news there." Tell me more. What is your reference for this?
Simon Klemperer
Hi Simon! In the future (a week or two), Farallon (and Scotia) will have disappeared because we returned them to the local SPCA for adoption - oceanic plates are actually a pretty great analog for foster kittens in that way.
Regarding your PS, Kyle has added a response to your question at the end of the post, with a figure of part of Japan showing events in the JMA catalog below volcanoes, at ~20-40 km - presumably associated with magma plumbing systems. We don't have a reference for this, though; if you run into one, please send it our way!
Once again Earthquake Insights shows the power of scientific communication without the filter of a 6-12 month delay bandpass imposed by publication in the modern scientific literature. Judith and Kyle are to be complimented once again on their thought-stimulating writing!
Using eQuakes to scan the Global CMT dataset, one can see many candidate structures that admit to the hypothesis that the subducting slab is tearing, on deeply biting ~N-S to ~NNW-SSE faults and/or shear zones, with right-lateral sense of movement in a direction not too different from the slab dip. There is one movement picture that makes such a pattern self-explanatory, and that is if the rate of south-directed rollback increases westward, with jumps in the rate of retreat accommodated by these newly forming slab tears. Naturally, such tears propagate ruptures upwards into the overlying crustal material, and are vitally important in hindering the lateral growth of the rupture extent of the different megathrust events that occur from time to time.
Interesting, in the hinge regions, such differential movement will result in compressive stress parallel to the arc, and the deviatoric stress axes in the shear zones facilitating the tearing process will be oriented with sigma1 plunging west, and sigma3 plunging NW. In this case ductile failure (governed by the maximum moment yield condition) predicts right-lateral strike-slip faults that deep moderately steep eastward.
Most major strike-slip faults (such as the Anatolian system) are controlled by deep structures, with surficial faults spinning as they propagate upward. This is as to be expected as they adjust to the Coulomb-Mohr Yield Condition that applies to more surficial levels.
Bottom line, thanks for drawing my attention to this.
This discussion is important to trying to understand similar, but infrequent large events that have historically (since seismographs were first installed in the NW) under south central Puget Sound where the subducting Juan de Fuca plate is being forced to twist by advancing North America. In 1939, 1949, 1965, and 2001 there have been Benioff events that have cumulatively killed and hurt people and done billions of dollars of damage. Notably in Seattle the Alaska Way Viaduct was torn down and replaced with a tunnel. The 1949 event was m=>7.0, making it especially dangerous. Understanding this activity becomes more approachable when examined in the context of the Alaska, Kamchatka, and Japan tectonic settings. It’s now 24 years since the last Benioff event and it can be safely asserted that probability of another in the near to very near future is increasing. Get ready to harvest data!!!
Dear Sir, thank you for your professional analysis and the information you provided.