Unraveling the complex structure of popocatepetl volcano (Central Mexico): New evidence for collapse features and active faulting inferred from geophysical data

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Highlights

  • Geophysical evidence unravels structure of the Popocatepetl volcanic complex.

  • Sector collapse features are constrained by magnetotellurics, aeromagnetics and gravity at Popocatepetl volcano.

  • Active faulting and structural weakness of the eastern flank of the volcano.

Abstract

Popocatepetl volcano located in central Mexico has been erupting since December 1994 and since then many studies have been carried out in order to understand its eruptive behavior and assess the volcanic hazard since more than 25 million people are at risk. Nevertheless, few geophysical studies have been conducted in order to image the structure of the volcano. For this reason, we carried out magnetotelluric and gravity surveys on the northern flank of the volcano and also modeled magnetic data for the area. In this paper we provide new insight into the structure of the northern part of this complex volcanic structure, which is made up of several volcanoes that had been camouflaged by later pyroclastic deposits from recent eruptions. Results show major northwest-and northeast trending faults in the area that displaced blocks toward the south. These scarps are related to sector collapses. The oldest part of the complex, the Tlamacas volcano was identified by the discontinuities inferred from gravity, magnetic and magnetotelluric data. Electrical resistivity distribution also shows the existence of a lack of continuity in a conductive horizon on the eastern side of the prospected area, which coincides with the location of the hypocenter of the May 6, 2013 earthquake. This feature also corresponds to the position of Tlamacas Volcano and its late dome, that is also faulted, confirming that the NE-SW trending fault is still active. Faulting inferred from geophysical data and confirmed by the occurrence of earthquakes and vent alignment suggests the structural control on magma ascent and the weakness of the southeastern flank of the volcano.

Introduction

Recent eruptions at Popocatepetl volcano began in 1994; since then, its activity has been monitored continuously, but the structure of the volcano and the underlying feeding system still need to be better constrained. The volcano (19.02°N, 98.62°W) is a large structure of dacitic-andesitic composition that covers over 500 km2 and has a crater that is 900 m wide. It is the second highest peak in Mexico (5454 m) and is located within a densely populated region in central Mexico approximately 70 km southeast of downtown Mexico City and 40 km west of the city of Puebla, making over 25 million people vulnerable to direct hazards associated with the volcano (Fig. 1). Due to the large exposed population, Popocatepetl poses the highest volcanic risk to the country (Mendoza-Rosas and De la Cruz-Reyna 2008). Its geologic past clearly indicates that it is capable of producing major eruptions since at least two Plinian events have occurred within the past 2000 years, affecting the human settlements in this area of central Mexico (Siebe et al. 1996; Martin-Del Pozzo et al. 1997).

The physical properties of a volcano can be partially inferred by studying seismic and other geophysical and geochemical data that can help define the structure and provide insight into the magmatic processes, an integrated approach that has been used at Popocatepetl (e.g. Martin-Del Pozzo 2012). However, from a structural approach, although some faults have been proposed for the area based on morphological and seismic criteria (e.g. De Cserna et al. 1988; Arámbula-Mendoza et al. 2010; Berger et al. 2011), most of them have not been mapped since there is little surface evidence and they are camouflaged by recent pyroclastic deposits.

Previous studies on Popocatepetl have focused principally on monitoring seismic activity, however, in order to understand the behavior of the volcano, its structure and evolution need to be further investigated. This paper is the first attempt to define the structures on the northern flank of Popocatepetl volcano through a comprehensive study integrating several geophysical techniques such as magnetotellurics, gravity and magnetics in order to better understand the construction processes and the structure of the Popocatepetl structure.

Section snippets

Geological setting

Popocatepetl is the youngest and southernmost volcano of the north-south trending Sierra Nevada volcanic ridge, which lies east of Mexico City. The present-day cone was built up in the last ~23,500 14C y BP after an older volcano collapsed producing a huge debris avalanche to the south (Macías-Vázquez et al. 1995; Siebe et al. 1995; Siebe et al. 2017). Several debris avalanche deposits have been recognized to the southeast and southwest of the active cone (Robin and Boudal 1987; Siebe et al.

Previous geophysical studies at the Popocatepetl Volcano

A seismic monitoring network at Popocatepetl is operated by the Centro Nacional de Prevención de Desastres (CENAPRED) and the Universidad Nacional Autónoma de México (UNAM). Seismicity suggests that there are two main areas where stress accumulates, one beneath the crater and another one to the southeast. However, some of volcanotectonic earthquakes have been detected in the northern area where the event with the largest magnitude was located.

Earthquakes from 2 to 4 km under the crater are

Methodology

Three geophysical techniques were implemented in the northern sector of the volcano in order to define the internal structure of Popocatepetl volcano: magnetotellurics (MT), gravity and magnetic methods. The application of the MT technique to the study of active volcanoes is well known since it may be used to provide the electrical resistivity distribution associated with the feeding system or to define major structures related with the eruptive activity (e.g. Kagiyama et al. 1999; Sakkas et

Results and Discussion

A vertical section from the 3D geoelectrical inversion coinciding with the magnetic profile direction is shown in Fig. 2 with a trending approximately E-W (N83°E). The shallower layer is a high resistivity horizon with values greater than 200 Ohm-m. This layer that reaches a depth of approximately 400 m, is made up of breccias and lava flows covered by pyroclastic deposits from the recent cone; however, between sites Pop004 and Pop005 the layer thickens sharply, marking the fault scarp of the

Conclusions

Results from the electrical resistivity distribution obtained from MT as well as the potential field methods studies, reveal the faulted structure of the northern part of Popocatepetl volcano and the scar of the older volcano, which collapsed to the southeast and on which the later cones were built. The two gravimetric profiles show the existence of multiple faults that cut the profiles in several points that not only correlate with lineaments observed on the surface but also coincide with the

CRediT authorship contribution statement

Claudia Arango-Galván: Conceptualization, Methodology, Validation, Investigation, Resources, Writing - original draft, Visualization, Project administration, Funding acquisition. Ana Lillian Martin-Del Pozzo: Conceptualization, Investigation, Resources, Writing - original draft, Funding acquisition. Elsa Leticia Flores-Márquez: Methodology, Writing - review & editing, Validation, Resources, Funding acquisition. Tomás González-Morán: Methodology, Writing - review & editing, Visualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Financial support for fieldwork was provided by PAPIIT-IN109114 and PAPIIT-IN114811. Authors thank Gerardo Cifuentes-Nava, Amiel Nieto, Maria Elizabeth Sánchez, Alejandro Vázquez and Ricardo Garza for their collaboration during fieldwork. We also thank Amiel Nieto, Ulises Valencia and José Luis Salas-Corrales for their collaboration in processing the data. Authors also acknowledge the Supercomputing Lab of SLECT from CICESE for allowing to use the cluster LAMB to perform the 3D modeling of MT

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