SEAMOUNT SUBDUCTION AND SLOW EARTHQUAKE ACTIVITY IN THE GUERRERO SEISMIC GAP: INSIGHTS INTO TSUNAMI EARTHQUAKES AND ACCRETIONARY WEDGE PROPERTIES
The Guerrero seismic gap, along the Mexican subduction zone, is a tectonically complex region where diverse seismic phenomena—including tectonic tremors, low-frequency earthquakes (LFEs), and tsunami earthquakes—occur despite the absence of recent megathrust ruptures. This combination provides a natural laboratory for examining how structural and physical heterogeneities along the shallow plate interface control fault slip behavior.
We analyze two years of continuous ocean-bottom seismometer (OBS) data using a modified envelope cross-correlation method for tremors and a matched-filter approach for LFEs. Slow earthquakes cluster near the trench in areas marked by rugged seafloor and positive residual gravity anomalies, implicating subducting seamounts. Their shallow depths and low-frequency spectral content suggest stable or conditionally stable sliding on the shallow megathrust.
The Mw 6.7 tsunami earthquake of April 18, 2002 exemplifies this behavior. Despite its moderate size, it produced a small tsunami and displayed slow rupture (~1 km/s), long duration (~70 s), weak high-frequency radiation, and an irregular moment rate function. Waveform analyses indicate rupture initiation at a subducted seamount with unilateral trench-parallel propagation. Its rupture area overlaps a ~50 mGal positive gravity anomaly, coinciding with tremor and LFE clusters, implying mechanical weakening of the accretionary wedge.
Further downdip, a broad negative gravity anomaly (~–50 mGal) corresponds to a lack of seismicity, possibly reflecting high porosity and fluid content that reduce plate coupling.
These findings underscore the role of subducting seamounts in shaping fault slip behavior and partitioning the megathrust into aseismic and tsunamigenic segments. The Guerrero gap illustrates how integrating slow earthquake patterns with geophysical imaging offers critical insights into interface heterogeneity and hazard potential in subduction zones.