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When - Although ETS alone will not help us predict an earthquake at this time, ETS may provide the basis for improved forecasting. Each ETS episode adds a small amount of stress on the locked portion of the subduction zone. This implies that as the stress level increases with each ETS event, one of them could trigger a great earthquake. Therefore, the likelihood of a great earthquake is enhanced during ETS. However, since ETS episodes of various sizes occur at different times all up and down the full length of the Cascadia subduction zone, we cannot yet say which ETS event will be the likely trigger.
Researchers are investigating possible relationships between the many other earthquakes that occur off the subduction fault in both the North America and Juan de Fuca plates, and the location and timing of ETS.
Originally posted by UdonNiedtuno
Originally posted by zworld
Does the lack of deep tremors in the middle of this zone indicate energy storage?
To clarify, does this image make you think that if a big quake were to hit soon, that it would be centered around Portland? I still haven't strapped my house to the foundation! I suppose I better get on that...
Originally posted by TrueAmerican
But notice all those real deep quakes in blue! Japan looks like it's about to be ripped apart or something.
Originally posted by muzzy
trees creaking in the wind probably make as much noise
is there any significance to them at all
Tremor is the seismic signature of a slow earthquake on the subducting plate interface. As the plates slowly slip past one another, they generate seismic noise that is quite different in its nature from normal earthquakes. The have lower frequency energy, and can last for minutes, hours, or even weeks.
These tremors are deep, non-volcanic signals associated with plate motion, not magmatic motion
What are the depths of these tremors?
This is a topic of ongoing research. We know that they occur deep, but the question is how deep? There are different bodies of evidence that suggest
1) They occur at the plate interface as direct result of the plate grinding on each other or
2) They are spread out above the plate boundary possibly occuring on faults that are readjusting in response to stress changes invoked by the slow slip on the plate inteface below.
What are the mangitudes of these tremors?
Small. We don't currently compute magnitudes as part of our automatic processing, but the small amplitudes associated suggest magnitudes < 2.
The epicenters shown are the result of an automated process that does not search for origin times, but instead looks for tremor in every 5-minute window overlapping each other by 2.5 minutes. The non-impulsive, emergent nature of tremor signals makes it difficult and computationally intensive to confidently identify origin times.
Because the signal is so different from regular earthquakes, traditional methods for automatically computing magnitudes are insufficient for deep, tectonic tremors. This is still an active area of research at the UW, and we hope to develop a reliable method for assigning magnitudes to epicenters using the observed amplitudes of these noisy signals.
Originally posted by Olivine
As to why there is very little tremor in central Oregon:
1. it could be freely slipping, therefore no tremor
2. plate interface is completely locked in this central portion of the CSZ. If this is the case, why wouln't slip occur farther east? They have quite a bit of equipment in the area that would pick up the tremor.
If the area in central Oregon is slipping freely, then would it follow that the "locked" area immediately west (at depths of 0-20km,say) has more stress being applied to it?