Characterization of fracture systems using precise array locations of earthquake multiplets: An example at Deception Island volcano, Antarctica

Abstract

[1] Volcano-tectonic earthquakes are common seismic events in active volcanic areas. The stress produced by volcanic processes is released through fracturing of the shallow crust. Very often, these earthquakes occur in multiplets with similar waveforms, a fact which indicates common source characteristics. In this work, we introduce a method that uses array techniques to calculate precise relative locations of earthquake multiplets. We use the relative slowness estimate method to determine accurately the apparent slownesses and propagation azimuths of the earthquakes relative to a selected master event.We also obtain precise estimates of the S-P delays. This information is used to calculate precise relative locations by ray tracing in an Earth model. We applied this method to determine the characteristics of the fractures activated during the 1999 seismic series at the Deception Island volcano, Antarctica. We selected a set of 17 earthquake multiplets, initially located in a small (4 × 4 km) region a few km NE of the array site. We estimated precise locations for 14 of the clusters. In most cases, hypocenters were distributed in well-defined planar geometries. We found the best fitting planes, which we interpreted as fractures in the medium. For two clusters, the method spatially separated the earthquakes into two subgroups. Thus, we obtained two planes for each of these clusters, resulting in a total of 16 fracture planes. This is the first time that the orientations of fracture planes related to a seismic series have been obtained using a seismic array. We performed several tests to check various aspects in relation to the stability of the method and concluded that the results were robust. The dip angles indicate that the planes are mostly subvertical, while the strike angles clearly show a NW-SE trend for most of the planes and a few planes with NE-SW trends. The geometry and position of these planes suggest that the 1999 seismic series was influenced by regional tectonics, although the origin of the destabilization of the system may be related to the reactivation of a shallow magma chamber.

The 3D Attenuation Structure of Deception Island (Antarctica)

“…The study of the seismic activity of the volcano is probably the most active and productive research line, as reported by Tejedo et al (2014). There are many results that help us better understand the dynamic and volcanological framework of the area, such as Vila et al (1992), , Ibáñez et al (1997Ibáñez et al ( , 2000Ibáñez et al ( , 2003, Saccorotti et al (2001), Martinez-Arevalo et al (2003), Benitez et al (2007), Carmona et al (2010Carmona et al ( , 2012Carmona et al ( , 2014, and García-Yeguas et al (2010). One of the objectives of these seismic studies is to provide 2D or 3D structure of the area, by using active or passive data as has been done by Ben-Zvi et al (2009), Zandomeneghi et al (2009), and Prudencio et al (2013).…”

Shallow structure of Deception Island, Antarctica, from correlations of ambient seismic noise on a set of dense seismic arrays

“…These swarms contained small earthquakes, with magnitudes of below 3. They occurred mostly along fracture systems trending NE–SW (Vila et al 1992; Ibáñez et al 2003a), but with a variety of source mechanisms reflecting a complex relationship with subsurface magma motions (Ibáñez et al 2003b; Carmona et al 2010).…”

“…Another clue that may help us with the interpretation of the differences between models F1 and F2 comes from the work of Carmona et al (2010). They investigated the geometry of the fault planes involved in the 1999 seismic series of Deception Island volcano (Ibáñez et al 2003a) located under the northern half of Port Foster.…”

Reply to comment from Blanco et al. (2015) on “Evidence from acoustic imaging for submarine volcanic activity in 2012 off the west coast of El Hierro (Canary Islands, Spain) by Pérez et al. [Bull. Volcanol. (2014), 76:882–896]

“…In reference to the array analysis from Blanco et al (2015), the information provided is vague and inconsistent, because some of the most important data to be given are the geometries and resolutions of the seismic antennas Almendros et al 1999;Almendros et al 2000;Ibáñez et al 2000;Saccorotti et al 2001;Almendros et al 2004;Carmona et al 2010). Depending on its geometry, an array will have preferential directions of resolution, and in Blanco et al (2015), this information is missing, and therefore, we cannot determine whether the absence of information is due to the absence of signals or to limitations in the resolution of the instruments.…”