Crust and subduction zone structure of Southwestern Mexico

Abstract

Southwestern Mexico is a region of complex active tectonics with subduction of the young Rivera and Cocos plates to the south and widespread magmatism and rifting in the continental interior. Here we use receiver function analysis on data recorded by a 50 station temporary deployment of seismometers known as the MARS (MApping the Rivera Subduction zone) array to investigate crustal structure as well as the nature of the subduction interface near the coast. The array was deployed in the Mexican states of Jalisco, Colima, and Michoacan. Crustal thickness varies from 20 km near the coast to 42 km in the continental interior. The Rivera plate has steeper dip than the Cocos plate and is also deeper along the coast than previous estimates have shown. Inland, there is not a correlation between the thickness of the crust and topography indicating that the high topography in northern Jalisco and Michoacan is likely supported by buoyant mantle. High crustal V p /V s ratios (greater than 1.82) are found beneath the trenchward edge of magmatism including below the Central Jalisco Volcanic Lineament and the Michoacan-Guanajuato Volcanic Field implying a new arc is forming closer to the trench than the Trans Mexican Volcanic Belt. Elsewhere in the region, crustal V p /V s ratios are normal. The subducting Rivera and Cocos plates are marked by a dipping shear wave low-velocity layer. We estimate the thickness of the low-velocity layer to be 3 to 4 km with an unusually high V p /V s ratio of 2.0 to 2.1 and a drop in S velocity of 25%. We postulate that the low-velocity zone is the upper oceanic crust with high pore pressures. The low-velocity zone ends from 45 to 50 km depth and likely marks the basalt to eclogite transition.

Fault‐Associated Magma Conduits Beneath Volcán de Colima Revealed by Seismic Velocity and Attenuation Tomography Studies

“…Based on the obtained results and other available information, we propose a scenario of magma feeding, schematically shown in Figure . According to the estimates by Suhardja et al () based on the receiver function analysis, the Moho depth beneath the CVC is about 40–42 km. Thus, the velocity structures observed at 60‐km depth correspond to the uppermost mantle.…”

“…SKS splitting analysis has revealed azimuthal anisotropy, which has provided evidence for slab tear beneath the CR (Soto et al, ). Suhardja et al () derived information about the Moho depth beneath the south‐western Mexico using receiver function analysis. Regional heterogeneities beneath the Rivera region were also investigated with the use of ambient noise tomography (Castellanos et al, ; Spica et al, ).…”

Rapid Evolution of Subduction‐Related Continental Intraarc Rifts: The Taupo Rift, New Zealand

“…The current rift is at a late stage 1 (based on observations from Acambay graben; Figure and Table ). Most of the deformation is still accommodated by the rift‐bounding faults, compared to faults at the graben axis (e.g., Langridge et al, , ; Suter et al, ; Ortuño et al, ), and the crust is still thick (40–50 km) (Suhardja et al, ; Urrutia‐Fucugauchi & Flores‐Ruiz, ). However, coeval volcanism and faulting in the graben axis (Sunye‐Puchol et al, ; Suter et al, ) suggests that extension is also partially accommodated by dike intrusion, indicating that the rift is evolving toward stage 2.…”

Crustal Deformation Following Great Subduction Earthquakes Controlled by Earthquake Size and Mantle Rheology

“…Coseismic and postseismic deformation of the 1995 M w 8.0 Jalisco earthquake. Depth below sea level of the megathrust, based onPardo and Suarez (1995) andSuhardja et al (2015), is contoured at 10-km intervals (light violet dashed lines). (a) Observed(Melbourne et al, 1997) and model-predicted horizontal coseismic displacements using the shown slip distribution.…”