Summary A temporary array of seven ocean bottom seismometers (OBS) was deployed offshore the Guerrero subduction zone in Mexico to monitor previously unreported shallow seismicity. These OBS instruments are especially valuable for studying earthquake activity in the Guerrero seismic gap, where a future large event could severely impact densely populated regions of Mexico. This study investigates the shallow seafloor structure, including site effects, shear wave attenuation, and velocity models, using both earthquake data and ambient seismic noise. We employed spectral inversion to estimate the quality factors of shear wave attenuation and site effects. Additionally, we calculated the microtremor horizontal-to-vertical spectral ratio (HVSR) as a proxy for site response and invert it using constraints from hydroacoustic seafloor profiles, parametric sub-bottom profile system (TOPAS), to derive the shallow velocity structure beneath the stations. The inclusion of TOPAS data in the inversion significantly improved convergence, reduced misfit, and resulted in more reliable subsurface models. The HVSR inversions indicate the presence of water-saturated sediments within the upper 250 m, characterized by shear-wave velocities ranging from 55.2 to 1950 m/s and Vp/Vs ratios between 1.80 and 27.84. Strong attenuation effects, typical of marine environments, were observed, with Q(f) values as low as Q = 86f0.62 in the forearc accretionary wedge. Our attenuation estimates are consistent with those found in other offshore subduction zones, contributing to a broader understanding of shallow structures in similar tectonic settings worldwide. We found strong agreement between the estimated site effects and HVSR results, underscoring their close relationship and supporting the reliability of our site response estimates. This is the first study in Mexico to use OBS data to characterize offshore attenuation, site effects, and velocity structure, information that will support future seismological analyses, including earth structure imaging and investigations of both large earthquakes and shallow slow earthquakes in the Guerrero seismic gap.
Plata‐Martínez et al. (Sat,) studied this question.