Spontaneous harmonic tremor on the San Jacinto fault, southern California

Gregor Hillers, & Jean-Paul Ampuero

Submitted 2011, SCEC Contribution #1502

The San Jacinto fault (SJF) is the most active branch of the San Andreas fault system in southern California. Although tectonic tremor---a low amplitude seismic signal frequently observed at deep sections of mature faults---has sporadically been triggered in the SJF area by distant large earthquakes, recurrent spontaneous tremor activity on this fault has escaped previous detection. Here we present observational evidence of episodic tectonic tremor associated with the Anza segment of the SJF, therefore extending the range of tectonic environments known to produce tectonic tremor to a structurally complex deformation zone. We resolve an irregular tremor activity over the two-year observation period, and the likely concentration below seismogenic depths signals deep transient deformation. In contrast to the broad spectral content of tremor sources identified in other regions, the SJF tremor is quasi-harmonic. Narrow-band spectra peaking at 3-4~Hz suggest, by analogy to volcanic tremors, a more active role of fluid flow in the source process of tectonic tremor than previously recognized.

Hillers, G., & Ampuero, J. (2011). Spontaneous harmonic tremor on the San Jacinto fault, southern California. Nature Geoscience, (submitted).