An integrated structural and GPS study of the Jalpatagua fault, southeastern Guatemala

Abstract

The Jalpatagua fault in Guatemala accommodates dextral movement of the Central America forearc. We present new global positioning system (GPS) data, minor fault analysis, geochronological analyses, and analysis of lineaments to characterize deformation along the fault and near its terminations. Our data indicate that the Jalpatagua fault terminates at both ends into extensional regions. The western termination occurs near the Amatitlan caldera and the southern extension of the Guatemala City graben, as no through-going structures were observed to continue west into the active volcanic arc. Along the Jalpatagua fault, new and updated GPS site velocities are consistent with a slip rate of 7.1 ± 1.8 mm yr−1. Minor faulting along the central section of the fault includes: (1) N-S–striking normal faults accommodating E-W elongation; and (2) four sets of strike-slip faults (oriented 330°, 020°, 055°, and 295°, parallel to the Jalpatagua fault trace). Minor fault arrays support dextral movement along a major fault in the orientation of the Jalpatagua fault. GPS and fault data indicate that the Jalpatagua fault terminates to the east near the Guatemala–El Salvador border. Data delineate a pull-apart basin southeast of the fault termination, which is undergoing transtension as the Jalpatagua fault transitions into the El Salvador fault system to the east. Within the basin, minor faulting and lineations trend to the NW and accommodate NE-directed elongation. This faulting differs from E-W elongation observed along the Jalpatagua fault and is more similar to minor faults within the El Salvador fault system.

Deformation in Western Guatemala Associated With the NAFCA (North America‐Central American Forearc‐Caribbean) Triple Junction: Neotectonic Strain Localization Into the Guatemala City Graben

“…Specifically, both regional block models indicate that sinistral slip rates across the Polochic‐Motagua fault system decrease from 11 to 13 mm/yr just north and west of the Guatemala City graben to 3 mm/yr or less along the Motagua fault directly west of the Guatemala City graben and the Polochic fault at the northern limit of the western Guatemala wedge (Figures 6b and 11 in Ellis et al., 2019). Both models also predict ∼7–8 mm/yr of dextral slip along the Jalpatagua fault east and south of the Guatemala City graben, diminishing to ∼2 mm/yr of distributed dextral offset between the CAFA and the backarc—with no evidence of a discrete fault—immediately west of the Guatemala City graben (Figure 7b in Ellis et al., 2019; and Figure 9b in Garnier et al., 2020). Both models thus identify the Guatemala City graben as the western limit of the extending end of the Caribbean plate.…”

“…(2019), Garnier et al. (2020), and Legrand et al. (2020) for information about the geodetic constraints on the tectonics elsewhere in northern Central America and southern Mexico.…”

“…The dextral Jalpatagua fault in southeastern Guatemala is the main boundary between the Caribbean plate and the CAFA. The western termination of the Jalpatagua fault occurs at or near the Amatitlán caldera, at the southern end of the Guatemala City graben (Garnier et al., 2020). There is no structure or geomorphic evidence for an active fault that could be the continuation of the Jalpatagua fault west of the Amatitlán caldera/Guatemala City graben.…”

“…The geodetic framework for this study and our related study of the nearby Jalpatagua fault (Garnier et al., 2020) is based on an updated elastic block model that assimilates new measurements at 32 GPS sites in northern Central America (locations are identified in Figure SA.1b in Supporting Information S1) into the regional model of Ellis et al. (2019), which was based on data as recent as early 2017.…”

“…The same approach was applied by Garibaldi et al (2016) in the Salvadoran volcanic arc. A more thorough explanation can be found in Garnier et al (2020) as applied to faulting in eastern Guatemala. In general, the direction of maximum elongation is determined by finding the orientation that maximizes the combined apparent heave of all faults along a transect, using the ratio between apparent heave and total heave (h app /h total ).…”