קולוקוויום בחוג לגאופיזיקה: What is this thing called tremor?
Allan Rubin, Princeton
Although tectonic tremor was discovered 2 decades ago, we still don't have a good physical picture of what is happening in the source region when it is generated. The Low Frequency Earthquakes (LFEs) that make up much of tremor are often thought to be generated by isolated, stick-slipping asperities within an otherwise creeping fault zone. Observations of tremor from southern Vancouver Island suggest an alternative. Over amplitudes that range from roughly the noise level on some tremor-free days to an order of magnitude larger, these tremor seismograms appear to be saturated with LFE arrivals, in the sense that inter-event times are typically shorter than characteristic LFE durations. Standard seismological techniques are not well-equipped to deal with such seismograms. If LFEs sample a time-invariant magnitude-frequency distribution with a random (Poissonian) distribution in time, then the amplitude of tremor velocity seismograms increases only as the square-root of the event rate, and loud tremor contains at least hundreds of LFEs per characteristic LFE duration. Coupled with good tremor locations, this likely implies too much slip to be consistent with geodetic constraints, suggesting that louder tremor is generated by larger rather than by more frequent LFEs. Comparison of observed tremor to synthetic seismograms built from LFE templates lead me to favor (for now) for a model in which LFEs are generated not by stick-slipping asperities, but by regions of the fault where the slip speed fluctuates at tremor frequencies, with amplitudes of fluctuation that increase with the average slip speed. But you shouldn't expect an answer to the question posed in my title.
מארגני האירוע: ד"ר רועי ברקן וד"ר אסף ענבל