Microseismic Magnitudes: Challenges in Determining the Correct Moment and Operating Regulatory Frameworks
A. Butcher, J. Kendall and R. Luckett
Event name: 81st EAGE Conference and Exhibition 2019
Session: Micro and Passive Seismic I
Publication date: 03 June 2019
Info: Extended abstract, PDF ( 2.74Mb )
Price: € 20
Magnitudes are an essential parameter for the estimation of source properties and the management of seismic risk, yet they are surprisingly difficult to accurately estimate. In this paper we show the challenges of working with microseismic events, and propose approaches to correct for some of the discrepancies that are commonly observed. Local magnitudes are regularly over-estimated at close hypocentral distances, and we present revised scales to correct for these discrepancy. As the magnitude decreases the frequency content of the source spectra would be expected to increase. This is however demonstrated not to be the case for microseismic events, which has an impact on the calculation of source properties and relationships between Local and Moment magnitude. We overcome this be adapting standard Brune source model to account for a preferential decay of high frequencies. This is used to derive a physics-based ML-MW relationship, and estimate the rupture radius and stress drop of a cluster of seismic events.