Coda Q before and after the eruptions of 13 November 1985, and 1 September 1989, at Nevado del Ruiz Volcano, Colombia

Abstract

Coda Q -1 was calculated at Nevado del Ruiz Volcano (NRV) before and after two phreatomagmatic eruptions (November 1985, September 1989 and for a period of stability (May 1987) using a functional form for coda derived from a single scattering model (Sato 1977). Substantial changes were found before and after the eruptions. The highest value of Q -1 was found during the November 1985 eruption, an intermediate value for the September 1989 eruption, and the lowest value for May 1987. It seems that the changes in coda Q -1 at NRV have a still-unknown relationship with the volume or magnitude of the eruption. A relatively strong frequency dependence was found for all periods. Also Q -1 clearly changed with time, suggesting that the scattering was strong for the eruption of November 1985 and decreased for the eruption of September 1989, and that the intrinsic absorption probably increased. This suggests the possibility that crystallization is taking place in the NRV magma. The clear change of coda Q -1 before and after the eruptions at NRV also suggests the possibility that coda Q -1 is a premonitory tool of activity at this volcano.

Seismic coda attenuation after the Mw = 6.2 Armenia (Colombia) earthquake of 25 January 1999

“…Londoño found that the scattering attenuation is the dominant attenuation process at low frequencies, whereas the intrinsic absorption is predominant for frequencies >6 Hz. Londoño's and our numerical results differ substantially which may be explained by the fact that Londoño [1996] Londoño et al [1998] studied a very small area (around 25 km in diameter and 20 km in depth) centered at the Nevado del Ruiz volcano, whereas our study focuses on a larger region. Figure 10 summarizes a comparison among the estimated intrinsic, scattering, and total attenuation parameters in several regions of the world, where solid circles represent the results of this study.…”

“…Recently, Hiramatsu et al [2000] confirmed temporal variations in Q c −1 and b value in Japan and concluded that Q c −1 can be a reliable indicator of stress changes in the crust if stable estimations are performed using a large number of stations. Also Londoño [1996] and Londoño et al [1998], who studied the Nevado del Ruiz volcano (which is part of the study area in the present work), reported significant changes in Q c −1 related to the level of volcanic activity. These observations suggest that Q c −1 may be used as an empirical tool for earthquake prediction.…”

“…In this case, the earthquakes used are associated to the subduction of the Nazca plate beneath South America. On the other hand, to the best of our knowledge, the only attenuation studies carried out in this region are those of Londoño [1996] and Londoño et al [1998], who calculated Q c −1 in the specific zone of the Nevado del Ruiz volcano using the single‐scattering method of Aki and Chouet [1975] and Q i −1 , Q s −1 , and Q t −1 using the MLTW method of Hoshiba et al [1991]. Londoño found that the scattering attenuation is the dominant attenuation process at low frequencies, whereas the intrinsic absorption is predominant for frequencies >6 Hz.…”

“…However, although the coffee‐growing region is a very active area capable of generating moderate size earthquakes, there is a lack of measurements of seismic wave attenuation. Previous studies have been done in the specific zone of Nevado del Ruiz volcano concerning tomography [ Muñoz , 1992] and temporal variations in Q c [ Londoño , 1996; Londoño et al , 1998].…”

Spatial variation of coda wave attenuation in northwestern Colombia

“…To the best of our knowledge, Colombia is a country where no full‐scale systematic investigation of seismic coda attenuation has been conducted. Only some specific local regions have been studied: Londoño (1996) and Londoño et al (1998) studied temporal variations in Q c in the Nevado del Ruiz volcano, and Ugalde et al (2002) performed a detailed study of seismic wave attenuation in the central Colombian Andes using recordings of a destructive earthquake that took place in that region on 1999 January 25. On a larger scale, Ojeda & Ottemöller (2002) presented a tomographic map of Q Lg for Colombia.…”