Abstract
Chemical and isotopic analyses of waters from 4 thermal springs of the Guerrero Pacific coast, the most seismically active area in Mexico, were weekly performed during a period of 1.5 years (October 2002-March 2004). Within the same time interval more than 150 earthquakes with 3.5 ＜ M ＜ 5.3 occurred in the area. The data display several anomalies in Cl, SO4, δD and δ^18O, always immediately after an event, with a relaxation time of 3-4 weeks. The responses occurred only with earthquakes having an estimated epicentral site very close or almost coincident with the location of a spring. These results indicate that: 1) at least for earthquakes with M＜5.3 within the Guerrero ”seismic gap” there were no precursors in the chemical (ionic) and isotopic composition of thermal waters (on the weekly basis); 2) two groups of springs near Acapulco, Dos Arroyos and Paso Real, are sensitive to seismic activity and therefore further monitoring of these springs may help to unravel the mechanisms of the ”hydro-seismo-interaction” in the area.
Highlights
The search of short-term precursors of earthquakes has been mostly concerned with gases (e.g., King 1986; Thomas 1988; Igarashi and Wakita 1990; Toutain and Baubron 1999; Chyi et al 2005; Walia et al 2005; Yang et al 2005)
It can be seen if to compare the chemical variations with a histogram of annual precipitations (Fig. 2) based on the averaged data set from the Acapulco meteorological station (Atlas del Agua 1976)
We found that variations in the water chemistry for all groups of spring exceeded essentially the analytical error level and for two groups of springs showed a clear seasonal trend
Summary
The search of short-term precursors of earthquakes has been mostly concerned with gases (e.g., King 1986; Thomas 1988; Igarashi and Wakita 1990; Toutain and Baubron 1999; Chyi et al 2005; Walia et al 2005; Yang et al 2005). Toutain et al (1997) analyzed the bottled water from a mineral spring located 29 km from the epicenter. The source of water analyzed after the Kobe earthquake was a 100 m-deep well located about 20 km east of the epicenter. In both cases an increase in Cl concentration before the earthquake was observed. The anomalies started about 5 months before the M = 7.2 Kobe event and about 5 days before the M = 5.2 Pyrenean earthquake. Both effects were caused by the stress-strain induced mixing of waters from adjacent aquifers.
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