Active faults sources for the Pátzcuaro–Acambay fault system (Mexico): fractal analysis of slip rates and magnitudes <i>M</i><sub>w</sub> estimated from fault length

Abstract

Abstract. The Pátzcuaro–Acambay fault system (PAFS), located in the central part of the Trans-Mexican Volcanic Belt (TMVB), is delimited by an active transtensive deformation area associated with the oblique subduction zone between the Cocos and North American plates, with a convergence speed of 55 mm yr−1 at the latitude of the state of Michoacán, Mexico. Part of the oblique convergence is transferred to this fault system, where the slip rates range from 0.009 to 2.78 mm yr−1. This has caused historic earthquakes in Central Mexico, such as the Acambay quake (Ms=6.9) on 19 November 1912 with surface rupture, and another in Maravatío in 1979 with Ms=5.6. Also, paleoseismic analyses are showing Quaternary movements in some faults, with moderate to large magnitudes. Notably, this zone is seismically active, but lacks a dense local seismic network, and more importantly, its neotectonic movements have received very little attention. The present research encompasses three investigations carried out in the PAFS. First, the estimation of the maximum possible earthquake magnitudes, based on 316 fault lengths mapped on a 15 m digital elevation model, by means of three empirical relationships. In addition, the Hurst exponent Hw and its persistence, estimated for magnitudes Mw (spatial domain) and for 32 slip-rate data (time domain) by the wavelet variance analysis. Finally, the validity of the intrinsic definition of active fault proposed here. The average results for the estimation of the maximum and minimum magnitudes expected for this fault population are 5.5≤Mw≤7. Also, supported by the results of H at the spatial domain, this paper strongly suggests that the PAFS is classified in three different zones (western PAFS, central PAFS, and eastern PAFS) in terms of their roughness (Hw=0.7,Hw=0.5,Hw=0.8 respectively), showing different dynamics in seismotectonic activity and; the time domain, with a strong persistence Hw=0.949, suggests that the periodicities of slip rates are close in time (process with memory). The fractal capacity dimension (Db) is also estimated for the slip-rate series using the box-counting method. Inverse correlation between Db and low slip-rate concentration was observed. The resulting Db=1.86 is related to a lesser concentration of low slip-rates in the PAFS, suggesting that larger faults accommodate the strain more efficiently (length ≥3 km). Thus, in terms of fractal analysis, we can conclude that these 316 faults are seismically active, because they fulfill the intrinsic definition of active faults for the PAFS.

Geophysics for geothermal exploration. Directional-derivatives-based computational filters applied to geomagnetic data at lake Cuitzeo, Mexico

“…Along the length of the E-W Chapala-Tula fault system -a proto-continental rift for some authors (see above) -the general northward extension, the frequency of geothermal areas, the high average heat flow (≥80 mW m-2) and the average low dip of the domino fault-systems (lower than 70o between Morelia and lake Cuitzeo), make us suppose that the main E-W structures, coeval to the TMVB (8-10 Ma, and potentially already active during TMVB basement volcanism, >15 Ma, Mendoza-Ponce et al, 2018), find a decollement shear-zone at a depth of no more than 8-10 km (probably shallower) -at which level they flatten. On the other hand, being active since the construction of the TMVB, NW-to N-trending Basin&Range faults, older than 20 Ma and with a higher angle of dip, could reach deeper than 15 km: the imposition of the regional average high heat-flow in the area, some 10 Ma (or 15-18 Ma, depending on whether the TMVB basement volcanism is considered as a main player for heat-flow and E-W faults activation), only relatively affected their geometry.…”

“…The central part of the TMVB (99o-102oW) is characterized by major E-W intra-arc basins: from W to E, the Chapala, Cuitzeo, Acambay and Mezquital grabens, 8-10 Ma old (Garduño-Monroy et al, 1993;Rosas-Elguera et al, 1997), whose E-W to ENE-WSW bordering normal faults have mean Quaternary slip rate of <0.1 mm yr-1, characterizing the area with a ~N-S oriented extension of <5% (Suter et al, 1995a;Ferrari and Rosas-Elguera, 2000). Recent studies have proposed, for some of these structures, an age of 18 Ma (Mendoza-Ponce et al, 2018). Figure 2 shows the Acambay and Cuitzeo extensional areas.…”

Definición del campo de esfuerzos-deformación y sismotectónica del sistema de fallas Morelia-Acambay, México

“…Se trata de una franja de ~30 km de ancho responsable de las depresiones tectónicas de Zacapu, Cuitzeo y Acambay (Suter, 2001;Israde-Alcántara et al, 2010ay 2010b. Las fallas E-O de este sistema actuaron a partir del Mioceno medio-tardío (7-9 Ma), mientras que las fallas NNO-SSE del Oligoceno y Mioceno temprano se han reactivado sucesivamente, desplazando y controlando a las depresiones lacustres E-O (Garduño-Monroy et al, 2001, 2009Mendoza-Ponce et al, 2018). En algunos estudios (Suter et al, 1995b) el análisis cinemático indica que algunas fallas empezaron su actividad posiblemente en el Plioceno temprano con movimientos laterales izquierdos a transtensivos, para luego volverse progresivamente más extensionales.…”

Diffuse gases in soil of Araró-Simirao geothermal system, Michoacán, Mexico

“…The MAFS consists of a series of normal E-W and NE-SW faults that cut through the central part of the TMVB and are associated with tectonic lacustrine depressions, such as Chapala, Zacapu, and Cuitzeo (Garduño-Monroy et al, 2009). The tectonic basins are seismically active with large periods of recurrence related to the activity of the MAFS (Mendoza-Ponce et al, 2018). The E-W faults are approximately 7 to 9 Ma old and appeared during the Miocene with evidence of reactivation in paleoseismological records from the Pleistocene and in recent estimates of shallow earthquake hypocenters (<20 km; Mendoza-Ponce et al, 2018).…”

“…The tectonic basins are seismically active with large periods of recurrence related to the activity of the MAFS (Mendoza-Ponce et al, 2018). The E-W faults are approximately 7 to 9 Ma old and appeared during the Miocene with evidence of reactivation in paleoseismological records from the Pleistocene and in recent estimates of shallow earthquake hypocenters (<20 km; Mendoza-Ponce et al, 2018). In Cuitzeo, the system has hanging blocks in the northern and southern edges of the lacustrine basin, which form a graben in the western part and a half-graben in the eastern part of the basin (Fig.…”