Project Outcomes Report for Project "Non-volcanic Tremor in the Northern San Andreas Fault System". Award Number: 1460498 The goal of this project has been to undertake a comprehensive search for ambient tremor within the northern SAF system; to characterize the tremors? spatial, temporal and size properties, and to gain new insights into the process of tremor and its relationship to faults, earthquakes and stress/strain change. EXPLOSION in DATA: The tremor phenomena provides a wealth of new information on the inner workings of deep fault zones and their relationship to large earthquakes. Their favorable attributes have changed traditional paradigms on data collection, and an explosion in available digital seismic data has ensued. As part of a "Big-Data" effort to characterize the spatial and temporal distribution of ambient tremor throughout the Northern San Andreas Fault system, continuous seismic data from multiple seismic networks with contrasting operational characteristics and distributed over a variety of regions are being used. A shift in philosophy from saving only earthquake triggered snippets to digitally archiving all continuous data occurred as the new phenomena were being discovered. Continuous data saved on tape was also retrieved and made available on-line. DATA CHALLENGES: A myriad of masquerading noise, anthropogenic and natural-event signals must also be discriminated in order to characterize tremor accurately. These Data-science challenges and others that we have endeavored to overcome include: Large volume of data Large geographic region Heterogeneous data coverage Inconsistent meta-data Noisy and time-variable seismic time-series Development of reproducible and replicable data-science methods and code. Accomplishments: We have shown that data mining of archived seismic data for detecting, locating, and monitoring tremor extending as far back as late 1993 is entirely feasible. Our work has helped lay the groundwork for future research targeting specific zones of tremor for more detailed analyses and for studies using different analysis (e.g. array deployments and methods and/or LFE analyses). And our work has also established a basis for future development of a near-real-time monitoring capability for SAF system tremor. NEW NOVEL METHODS: Automated Meta-data Search, Assesment, and selection (pre-waveform) Automated work-arounds to address confounding Noise-types (e.g., Earthquakes, spikes, multi-station common mode noise, glitches, jogs, Gaps and Dead channels) (Fig.Noise, Detections and FDB filtering) Adaptive station-channel selection series: PDC, BDC, IDC, TIDC, FDC Cross-correlation rather than amplitude detection: Hits-O-Gram Detections: Detection-Duration Catalogs Amplitude-Transform-Stacks ? Percentile Stacking(Fig. Amplitude Transformations). Envelope Template approach QC-Ranking and Selection Median Filtering Duration Band Filtering (DBF) Travel-time alignments for locaitons Initial Locations, Grid-Search Final Locations Time-progressive, Multiple-Same-Tremor-Locations for investigating?tremor migration patterns More sensitive detection (x13) Solves daily noise cycle problem More sensitive detection (x13) Solves daily noise cycle problem No exhaustive pre-envelope development required (e.g. unlike LFEs) To smooth out spikes Automated median filtering methods that we have developed are flexible enough to work consistently over many years of evolving data collection quality. Various properties of median filtering over time and space are used to addresschallenges posed by the Non-volcanic tremor detection problem. Identifies and Redacts (windows out) Quakes, Jogs, Gaps and Glitches Improved Alignments, Timing Resolution and Multi-Episode Locations. DISCOVERIES: First Discovery of Tremor in the Geysers Region, Califnornia First Discovery of Tremor along the San Andreas Fault at Bitterwater, CA. The Earliest California Tremor ever found (Bitterwater Oct. 1993) (Fig. Earliest Tremor). Tremor Slow-slip excitation at 300 km distance ? the Napa Valley M6 and Extreme activation at Parkfield. Publications:

Delbridge, Brent G.; Nadeau, Robert M; Carmichael, Joshua D.; Burgmann, Roland; Geodetic Measurements of Slow Slip Events Southeast of Parkield, CA, (submitted to the JOURNAL OF GEOPHYSICAL RESEARCH, November (2019)). Zhang, HJ (Zhang, Haijiang);

Nadeau, RM (Nadeau, Robert M.); Guo, H (Guo, Hao) "Imaging the nonvolcanic tremor zone beneath the San Andreas fault at Cholame, California using station-pair double-difference tomography" EARTH AND PLANETARY SCIENCE LETTERS, v.460, p.76. doi:10.1016/j.epsl.2016.12.006 (2017).

Guo, H., H. Zhang, R. M. Nadeau, and Z. Peng, High-resolution deep tectonic tremor locations beneath the San Andreas Fault near Cholame, California, using the double-pair double-difference location method, J. Geophys. Res. Solid Earth, 122, 3062?3075, doi:10.1002/2016JB013919 (2017).

Naoki Uchida, Takeshi Iinuma, Robert M. Nadeau, Roland Burgmann, Ryota Hino "Periodic slow slip triggers megathrust zone earthquakes in northeastern Japan" SCIENCE, v.351, (2016), p.488.

Sammis, C.G., S.W. Smith, R.M. Nadeau and R. Lippoldt, Relating Transient Seismicity to Episodes of Deep Creep at Parkfield CA, Bull. Seismol. Soc. Am., 106, 1887-1899, doi:10.1785/0120150224, (2016).

Last Modified: 02/17/2020
Modified by: Robert M Nadeau