Non-Volcanic Tremor in South-Central Alaska and its Relation to the 1998-2000 Slow-Slip Event

The discovery, less than a decade ago, of non-volcanic tremor and slow slip events in the Cascadia subduction zone and in the Nankai trough, has led to an investigation of the phenomena at many tectonic plate margins. It now looks likely that slow-slip events and non-volcanic tremor are present in many, if not all subduction zones, in addition to other types of faults. Slow-slip events most likely play an important role in the seismogenic processes at subduction zones, by either loading locked portions of the interface, and/or perhaps in triggering major earthquakes on the plate boundary. Non-volcanic tremor appears to be a closely related phenomenon, which might be used as an indicator of aseismic creep, or changes in fluid or pore pressure, and perhaps shed light on the processes active in the deeper interplate transition zone. Here we examine non-volcanic tremor in south- central Alaska occurring simultaneously with a large slow-slip event that occurred in the region between 1998- 2000. We tabulate the observed non-volcanic tremor events in terms of durations, locations (when possible), and maximum amplitudes for three months of each year between 1998 and 2001. The majority of the non-volcanic tremor signals observed after the onset of the slow-slip event in March 1998 are bursts lasting between 10 and 15 minutes with frequencies ranging from 1-10 Hz. Similar signals lasting up to a day are also observed, but less frequently. By the summer of 2001 the quantity of non-volcanic tremor decreases dramatically from the previous summer. Episodes rarely last up to 10 minutes and maximum amplitudes are lower than previous years. The decrease in non-volcanic tremor activity in the summer following the end of the slow-slip event is the first evidence that the relationship between slow-slip events and non-volcanic tremor seen in Cascadia and southwest Japan may also exist in central Alaska.