Variable Slow Slip Speeds at Sub-Daily Timescales: Constraints From High-Rate GPS Records

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Episodic tremor and slow slip events (ETS) have been observed in many studies as a several-day-long transient on daily GPS positions with net horizontal offsets of ~5 mm. The tremor record is suggestive of sub-daily signals of discontinuous slip, which are not captured by daily solutions. For example, Hawthorne et al., (2016) used strainmeters to show that rapid tremor reversals (RTRs) represent 10-20% of the slow slip moment. By studying sub-daily signals, we hope to observe discontinuous behavior in slow slip, suggested by the tremor record. We use Track, a high-rate GPS processing package within GAMIT (Herring et al., 2010) to find 1 Hz solutions. We chose several GPS stations on the Olympic Peninsula from PANGA and PBO. These stations are located above the strongest tremor signals during the 2010 ETS event (8/18 - 8/19), based on tremor locations from the PNSN. We solve for the positions on the horizontal components relative to a reference station on stable North America. One of the challenges of using high-rate GPS is the increased noise, which is averaged out in daily positions. We process the raw positions by removing significant outliers (Bock et al., 2000) and using sidereal filtering (Nikolaidis et al., 2001) to remove any repeatable noise sources. Additionally, Langbein & Bock (2004) found that they could resolve 2 mm of offset by averaging 1 min of data, suggesting that further averaging might allow for the observation of smaller signals. We use forward modeling to determine what potential sub-daily signals from the tremor record, such as RTRs, would look like in a high-rate GPS record and whether that signal would be above the noise level. We attempt to observe sub-daily nuances of slow slip, such as accelerating and decelerating. These potential observations will help better characterize the source physics behind slow slip and tremor.

Presenting Author: Kelley Hall

Authors