Action 2.7 : Magnitude and focal depth in instrumental catalogues

Develop methods to refine instrumental magnitude and focal depth of small-magnitude events in low-to-moderate seismicity areas

Motivations

In regions of low-to-moderate seismic activity, catalogues are mainly composed of small magnitude events. This population of events can then be used, for instance, to constrain recurrence laws for seismic hazard assessment. Depending on the instrumentation used for the recording of such small-magnitude earthquakes, biases may appear in seismic moment estimates. First, inhomogeneous network coverage can cause large uncertainties or bias in focal depth estimates. Second, weak low-frequency (LF) energy radiation for small-magnitude events question the pertinence of the classical approach used for moment-magnitude estimates (Brune, 1970).

Program of research

We propose to improve the methodology to estimate instrumental magnitude which is based on the quantitative modeling of the seismic energy envelop. This includes the radiation effects of the source, intrinsic attenuation and scattering. In fact, the modeling of the entire seismic envelop of the signal - direct and diffuse (or coda) waves – is the key to distinguish the source, site and propagation effects. These developments will benefit from the improved data coverage over France and from the high-quality seismic data delivered by the dense RESIF seismic network.

Mh estimation 1

  • Literature review and extraction of the seismic database (through RESIF) on which the method will be developed. Implementation of the Green’s function computed through a diffuse and absorbing medium adapted to the French context.
  • Development and implementation of the new automatic procedure to estimate the earthquake magnitude from the modeling of the entire envelop of the signal.
  • Comparison of the new seismic catalog produced in the thesis project with the SiHex catalog built through an empirical method.

Organization

  • Type: PhD project
  • Collaboration: EDF, CNRS/IRAP (Toulouse University), CEA (LDG)
  • Status: In progress (2018-2021)