Source parameters of small events using constrained deconvolution with empirical Green's functions

Abstract

An iterative and constrained deconvolution technique, called projected Landweber deconvolution (PLD), is applied to a local earthquake data set recorded in the southwestern Alps (NW Italy) in order to estimate the relative source time function (RSTF) of the events. The magnitude range analysed is 1.4<ML<4.3. The smallest events (ML<2.0) are used as empirical Green's functions (EGF) to deconvolve the larger earthquakes. The crucial choice of appropriate EGF is tackled using high-precision relative locations. Results demonstrate that PLD successfully overcomes the instability effects of the deconvolution process and provides stable and reliable RSTFs. Moreover, this method allows us to obtain an objective determination of the duration of the RSTF, which is essential to estimate correctly the source size. Combining the information inferred from both RSTFs and displacement spectra, source parameters are computed for all the events. We obtain seismic moments ranging from 2.9 × 1011to 3.1 × 1014N m and source radii between 70 and 700 m. Taking the instrumental limits into account, no breakdown in constant stress drop scaling is seen in our estimates.