Precursory seismicity of the 1994 eruption of Popocatépetl Volcano, Central Mexico

Abstract

Popocatépetl Volcano is located in the central Mexican Volcanic Belt, within a densely populated region inhabited by over 20 million people. The eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions, including Plinian events. After nearly 70 years of quiescence, Popocatépetl reawakened in December 21, 1994. The eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth-anddestruction episodes, similar to events that have apparently been typical for Popocatépetl since the fourteenth century. In this regime, the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence. In this paper we analyze five years of volcanotectonic seismicity preceding the initial eruption of the current episode. The evolution of the V-T seismicity shows four distinct stages, which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence. The thermal effects of a magma intrusion at depth, the fracturing related to the slow development of magma-related fluid pathways, the concentration of stress causing a protracted acceleration of this process, and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of V-T seismic energy release. A hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption. The total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes, limit that was reached by Popocatépetl before the eruption.

Understanding Fast and Slow Unrest at Volcanoes and Implications for Eruption Forecasting

“…Ash emissions have occurred since 1994; ash emitted in 1997-1998 contained olivine of Fo 84−86 , indicating involvement of mafic magma (Witter et al, 2005). A lava dome was emplaced in the crater on 25 or 26 March 1996(Delgado-Granados et al, 2001De la Cruz-Reyna et al, 2008). This was the first unequivocal indication of magma since the volcano had started its re-activation in early 1990 more than 6 years earlier.…”

“…The pH of the crater lake began to decline in 1992, followed by increases in lake water temperatures in 1993 and 1994. Fumarolic activity increased in 1993, and the first COSPEC measurement in February 1994 revealed an elevated SO 2 flux of ∼1,200 t/d (De la Cruz-Reyna et al, 2008). Ash emissions have occurred since 1994; ash emitted in 1997-1998 contained olivine of Fo 84−86 , indicating involvement of mafic magma (Witter et al, 2005).…”

“…This mechanism of opening is well-illustrated by the pattern of volcanotectonic earthquakes observed at Popocatépetl between 1990 and 1996 prior to the first arrival of lava at the surface (Figure 6). Exponential increases in earthquakes and seismic energy in 1992-1994 were likely the result of both new fractures and increased fracture densities as magma slowly made its way upward (De la Cruz-Reyna et al, 2008). Elevated SO 2 fluxes of 2,000-3,000 t/d in 1994-1996 showed that the plumbing system beneath the volcano had become comparatively open.…”

Strain‐induced permeability increase in volcanic rock

“…This is often accompanied by voluminous discharges of SO 2 after the onset of extrusive activity [e.g., Delgado-Granados et al, 2001], suggesting that networks of shear fractures allow efficient outgassing to occur. Lengthening repose times between successive Vulcanian eruptions-as observed at Soufrière Hills Volcano [Herd et al, 2005] and Popocatépetl, Mexico [Delgado-Granados et al, 2001;De la Cruz Reyna et al, 2008], for example-show that the threshold pressure required for explosive failure [e.g., Melnik and Sparks, 2002;Koyaguchi et al, 2008] becomes progressively more difficult to attain [Edmonds and Herd, 2007].…”

High‐Broadband Seismoacoustic Signature of Vulcanian Explosions at Popocatépetl Volcano, Mexico

“…After nearly 70 years of quiescence, Popocatépetl underwent a significant reactivation in December 1994 and since then its eruptive activity has been dominated by hydrothermal processes and magmatic degassing, characterized by periodic emissions of gas and ash, occasional Vulcanian explosions, episodic passive effusions of lava, and the extrusion and destruction of lava domes. All of these eruptive dynamics result in abundant seismicity, including long‐period and very‐long‐period events, tremor, and explosion signals (Arciniega‐Ceballos et al, , , , , ; Arámbula‐Mendoza et al, ; Chouet et al, ; De la Cruz‐Reyna et al, ; Roman, ). This activity is associated with rumbling and roaring sounds that can commonly be heard in different localities within about 20 km surrounding Popocatépetl (and occasionally farther, e.g., Puebla, 45 km, presumably for larger explosions and as propagation conditions such as wind direction allow).…”