Moment‐Duration Scaling of Low‐Frequency Earthquakes in Guerrero, Mexico

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 M0∼3×1012 N.m (Mw∼2.3) and fc∼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.

Does Deep Tectonic Tremor Occur in the Central‐Eastern Mediterranean Basin?

“…5). Similar Mw LFEs or larger have been documented at several fault systems around the Pacific rim, including the Guerrero trench in Mexico (Mw 1.7-3 with a few events up to Mw 3.5, Farge et al, 2020), the Cascadia Subduction Zone (Mw 1.0-2.6, Bostock et al, 2015), the Parkfield-Cholame segment of the San Andreas Fault (Mw 1.6-1.9, Fletcher & McGarr, 2011), and the Nankai trench in Japan (Mw 0.9-2.2, Supino et al, 2020). Previous studies have noticed lower Mw LFEs obtained from amplitude ratios with local earthquakes, which may underestimate LFE magnitudes due to differing frequency contents relative to local earthquakes (e.g.…”

“…We therefore report Mw values estimated from source parameter analysis and not those obtained by relative amplitude ratios. In the case of Peloponnese, during the SSE in 2014-2015 we would still be able to detect very vigorous tremor episodes composed by LFEs with similar Mw values to that of the largest recorded ones in Cascadia by Bostock et al (2015) or at the Guerrero trench by Farge et al (2020), while the network configuration and ambient noise level would have potentially missed tremor-like signals during the 2018 SSE. However, due the high similarity of the duration, location, and released seismic moment of the 2014-2015 and the 2018 SSEs (Mouslopoulou et al, 2020) it is possible that the absence of vigorous tremor episodes is common to both the SSEs.…”

“…Mw refers to values for individual LFEs comprising the tremor episodes. For reference, the dashed horizontal lines indicate the Mw of the largest detected LFEs within tremor episodes at several fault systems around the Pacific rim, including the Guerrero trench (Fa20, Farge et al, 2020), the Cascadia Subduction Zone (Bo15, Bostock et al,2015), the San Andreas Fault (F&M11, Fletcher & McGarr, 2011) and the Nankai trench (Su20, Supino et al, 2020).. KTF, Kefalonia Transform Fault; CSZ, Calabrian Subduction Zone; HSZ, Hellenic Subduction Zone; NAF, North Anatolian Fault. For more details on the synthetic tests performed to estimate the magnitude thresholds refer to Text S2.…”

Episodicity and Migration of Low Frequency Earthquakes modeled with Fast Fluid Pressure Transients in the Permeable Subduction Interface

“…These shortcomings may be limiting in subduction zones because the brittle-to-ductile transition proceeds over an increasingly wide off-fault region as depth increases [73]. Source dimensions for tremor and LFEs are typically inferred to be a few hundred meters [e.g., 23,31,92], close to the thickness of the highly deformed permeable fault zone [e.g., 4]. This calls for more complete models dealing with processes in the interior of these zones.…”

“…Furthermore, the sources of seismic and geodetic events are not always co-located [e.g., 57]. In addition, in some subduction zones, LFEs do not conform to the moment-duration scaling of classical shear rupture [20,31]. One should finally note that the predominance of S-waves in the seismic signals does not necessarily establish a shear rupture mechanism.…”