A local magnitude scale for a volcanic region: the Canary Islands, Spain

In this study, we define a local magnitude scale for earthquakes occurring in the Canary Islands during the 2003–2020 period. We used data corresponding to 696 earthquakes (excluding those associated with the 2011–2015 El Hierro eruption), which consisted of 9267 observations in a hypocentral distance in the range of 10–500 km. Amplitudes were obtained by deconvolving the original recordings with the instrument response and then convolving the recording with the Wood-Anderson response. The amplitudes were inverted simultaneously to obtain the distance correction terms and station corrections. We found that the amplitude for this set of data is linearly attenuated. However, this is not the case for the seismicity recorded during the 2011 El Hierro eruption, which is the reason for excluding data for that case. We obtain a local magnitude of ML = log A + 0.967 log (R/40) + 0.00142 (R − 40) + 2.445 + S, where A is the maximum amplitude in millimeters of the S wave for the horizontal components of the simulated Wood-Anderson instrument (WA), R is the hypocentral distance in kilometers, and S is the station correction for each component at every station. This relationship indicates that seismic waves at this island volcano setting are less attenuated than those in crustal continental settings, such as across the Iberian Peninsula or in California.