@article{fdi:010075663,
  title = {{T}he rupture extent of low frequency earthquakes near {P}arkfield, {CA}},
  author = {{H}awthorne, {J}. {C}. and {T}homas, {A}. {M}. and {A}mpuero, {J}ean-{P}aul},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he low frequency earthquakes ({LFE}s) that constitute tectonic tremor are often inferred to be slow: to have durations of 0.2-0.5 s, a factor of 10-100 longer than those of typical {M}-{W} 1-2 earthquakes. {H}ere we examine {LFE}s near {P}arkfield, {CA} in order to assess several proposed explanations for {LFE}s' long durations. {W}e determine {LFE} rupture areas and location distributions using a new approach, similar to directivity analysis, where we examine how signals coming from various locations within {LFE}s' finite rupture extents create differences in the apparent source time functions recorded at various stations. {W}e use synthetic ruptures to determine how much the {LFE} signals recorded at each station would be modified by spatial variations of the source-station traveltime within the rupture area given various possible rupture diameters, and then compare those synthetics with the data. {O}ur synthetics show that the methodology can identify interstation variations created by heterogeneous slip distributions or complex rupture edges, and thus lets us estimate {LFE} rupture extents for unilateral or bilateral ruptures. {T}o obtain robust estimates of the sources' similarity across stations, we stack signals from thousands of {LFE}s, using an empirical {G}reen's function approach to isolate the {LFE}s' apparent source time functions from the path effects. {O}ur analysis of {LFE}s in {P}arkfield implies that {LFE}s' apparent source time functions are similar across stations at frequencies up to 8-16 {H}z, depending on the family. {T}he interstation coherence observed at these relatively high frequencies, or short wavelengths (down to 0.2-0.5 km), suggest that {LFE}s in each of the seven families examined occur on asperities. {T}hey are clustered in patches with sub-1-km diameters. {T}he individual {LFE}s' rupture diameters are estimated to be smaller than 1.1 km for all families, and smaller than 0.5 km and 1 km for the two shallowest families, which were previously found to have 0.2-s durations. {C}oupling the diameters with the durations suggests that it is possible to model these {M}-{W} 1-2 {LFE}s with earthquake-like rupture speeds: around 70 per cent of the shear wave speed. {H}owever, that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence. {T}he data for that family are better matched if {LFE}s have rupture velocities smaller than 40 per cent of the shear wave speed, or if {LFE}s have different rupture dynamics. {T}hey could have long rise times, contain composite sub-ruptures, or have slip distributions that persist from event to event.},
  keywords = {{T}ransient deformation ; {E}arthquake source observations ; {R}heology and friction of fault zones ; {C}ontinental tectonics: strike-slip and ; transform ; {ETATS} {UNIS} ; {CALIFORNIE}},
  booktitle = {},
  journal = {{G}eophysical {J}ournal {I}nternational},
  volume = {216},
  numero = {1},
  pages = {621--639},
  ISSN = {0956-540{X}},
  year = {2019},
  DOI = {10.1093/gji/ggy429},
  URL = {https://www.documentation.ird.fr/hor/fdi:010075663},
}