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ABSTRACT Seismic and geodetic observations in subduction zone forearcs indicate that slow earthquakes, including episodic tremor and slip, recur at intervals of less than six months to more

than two years1,2. In Cascadia, slow slip is segmented along strike3 and tremor data show a gradation from large, infrequent slip episodes to small, frequent slip events with increasing

depth of the plate interface4. Observations5,6,7 and models8,9 of slow slip and tremor require the presence of near-lithostatic pore-fluid pressures in slow-earthquake source regions;

however, direct evidence of factors controlling the variability in recurrence times is elusive. Here we compile seismic data from subduction zone forearcs exhibiting recurring slow

earthquakes and show that the average ratio of compressional (P)-wave velocity to shear (S)-wave velocity (_v_P/_v_S) of the overlying forearc crust ranges between 1.6 and 2.0 and is

linearly related to the average recurrence time of slow earthquakes. In northern Cascadia, forearc _v_P/_v_S values decrease with increasing depth of the plate interface and with decreasing

tremor-episode recurrence intervals. Low _v_P/_v_S values require a large addition of quartz in a mostly mafic forearc environment10,11. We propose that silica enrichment varying from 5 per

cent to 15 per cent by volume from slab-derived fluids and upward mineralization in quartz veins12 can explain the range of observed _v_P/_v_S values as well as the downdip decrease in

_v_P/_v_S. The solubility of silica depends on temperature13, and deposition prevails near the base of the forearc crust11. We further propose that the strong temperature dependence of

healing and permeability reduction in silica-rich fault gouge via dissolution–precipitation creep14 can explain the reduction in tremor recurrence time with progressive silica enrichment.

Lower gouge permeability at higher temperatures leads to faster fluid overpressure development and low effective fault-normal stress, and therefore shorter recurrence times. Our results also

agree with numerical models of slip stabilization under fault zone dilatancy strengthening15 caused by decreasing fluid pressure as pore space increases. This implies that

temperature-dependent silica deposition, permeability reduction and fluid overpressure development control dilatancy and slow-earthquake behaviour. Access through your institution Buy or

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PHYSICAL CONDITIONS AND FRICTIONAL PROPERTIES IN THE SOURCE REGION OF A SLOW-SLIP EVENT Article 06 May 2021 OSCILLATIONS IN FLUID PRESSURE CAUSED BY SILICA PRECIPITATION IN A FRACTURE

Article Open access 20 February 2025 A LIKELY GEOLOGICAL RECORD OF DEEP TREMOR AND SLOW SLIP EVENTS FROM A SUBDUCTED CONTINENTAL BROKEN FORMATION Article Open access 16 March 2022 REFERENCES

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  Download references ACKNOWLEDGEMENTS Data used in this study come from the Japan Meteorological Agency, New Zealand National Seismograph Network, and the Tectonic Observatory (Caltech).

Funding for this work comes from the Natural Science and Engineering Research Council (Canada) and the Miller Institute for Basic Research in Science (University of California, Berkeley). We

thank N. Beeler, A. Rubin and P. Ampuero for discussions and comments. AUTHOR INFORMATION AUTHORS AND AFFILIATIONS * Department of Earth Sciences, University of Ottawa, Ottawa, Ontario K1N

6N5, Canada, Pascal Audet * Department of Earth and Planetary Science and Berkeley Seismological Laboratory, University of California, Berkeley, 94720-4767, California, USA Roland Bürgmann

Authors * Pascal Audet View author publications You can also search for this author inPubMed Google Scholar * Roland Bürgmann View author publications You can also search for this author

inPubMed Google Scholar CONTRIBUTIONS P.A. performed data processing and inversion. Both P.A. and R.B. contributed to the interpretations and preparation of the final manuscript.

CORRESPONDING AUTHOR Correspondence to Pascal Audet. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. EXTENDED DATA FIGURES AND TABLES EXTENDED

DATA FIGURE 1 EXAMPLES OF RECEIVER FUNCTIONS AND INVERSION RESULTS FOR EACH SUBDUCTION ZONE. In A–C the slab contours from refs 30 and 41 are in yellow, contours of slow-slip patches from

ref. 2 are in light green, contours and epicentres of tremors from ref. 2 are in purple, and station locations used in this study are shown as inverted red triangles. For a subset of

stations (PLAY, PXZ and IGK, identified by the blue squares on the maps) we show the observed (top, A) and modelled (bottom, B) radial receiver functions ordered by back-azimuth and, for

each back-azimuth, by slowness of the incoming P wave. C, A slice through model misfits, with warm colours indicating low values, showing the _v_P/_v_S of forearc crust versus the _v_P/_v_S

of the low-velocity zone. The star shows the minimum value of the misfit plot (best-fitting value). POWERPOINT SLIDES POWERPOINT SLIDE FOR FIG. 1 POWERPOINT SLIDE FOR FIG. 2 POWERPOINT SLIDE

FOR FIG. 3 RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Audet, P., Bürgmann, R. Possible control of subduction zone slow-earthquake periodicity by

silica enrichment. _Nature_ 510, 389–392 (2014). https://doi.org/10.1038/nature13391 Download citation * Received: 03 December 2013 * Accepted: 08 April 2014 * Published: 18 June 2014 *

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