Moment‐Duration Scaling of Low‐Frequency Earthquakes in Guerrero, Mexico. Issue 8 (4th August 2020)

• Record Type: Journal Article
• Authors: Farge, Gaspard; Shapiro, Nikolaï M.; Frank, William B.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 8(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-04
• Subjects: low‐frequency earthquakes -- self‐similarity -- Guerrero -- slow earthquakes -- Mexico; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2019JB019099
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: Low‐frequency earthquakes (LFEs) are detected within tremor, as small, repetitive, impulsive low‐frequency (1–8 Hz) signals. While the mechanism causing this depletion of the high‐frequency content of their signal is still debated, this feature may indicate that the source processes at the origin of LFEs are different from those for regular earthquakes. Key constraints on the LFE‐generating physical mechanisms can be obtained by establishing scaling laws between their seismic moment and source durations. Here we apply a simple spectral analysis method to the S waveforms of LFEs from Guerrero, Mexico, to measure their seismic moments and corner frequencies, a proxy to source duration. We find characteristic values of M 0 ∼3×10 12 N.m ( M w ∼2.3) and f c ∼3.0 Hz with the corner frequency very weakly dependent on the seismic moment. This moment‐duration scaling observed for Mexican LFEs is similar to one previously reported in Cascadia and is very different from the established one for regular earthquakes. This suggests that they could be generated by sources of nearly constant size with strongly varying intensities. LFEs do not exhibit the self‐similarity characteristic of regular earthquakes, suggesting that the physical mechanisms at their origin could be intrinsically different. Plain Language Summary: Low‐frequency earthquakes are unusual, small earthquakes that are detected on the deep end of plate boundary faults. They occur during periods of slow slip, when the plates start sliding against each other much slower than during earthquakes, but long enough to release the energy that might otherwise have caused large earthquakes. Thus, they carry precious information about the fault behavior while slow slip is active. In this study, we analyze a selection of low‐frequency earthquakes from a slow slip zone of the Mexican subduction, beneath the state of Guerrero. We find that their magnitude is on average higher than in other regions where they have been detected ( M w 1.5 – 3). We also find that whatever the magnitude of these events, they always last about 0.3 s. On the contrary, regular earthquakes are known to last longer when they grow larger, and low‐frequency earthquakes in Nankai (Japan) appear to behave similarly. We discuss a physical mechanism explaining such a discrepancy with regular earthquakes and such strong regional variations. The implication of crustal fluids circulating at extremely high pressure in between plates might be one of the key components of this mechanism, as it often is for slow slip processes. Key Points: Seismic moment‐duration scaling is analyzed for tectonic low‐frequency earthquakes in Guerrero, Mexico Corner frequencies, inversely proportional to source duration, are found to be very weakly dependent on seismic moment Low‐frequency earthquakes in Guerrero do not exhibit the self‐similarity of regular earthquakes