Reverse modelling for seismic event characterization

Abstract

S U M M A R YThe localization of seismic events is of utmost importance in seismology and exploration. Current techniques rely on the fact that the recorded event is detectable at most of the stations of a seismic network. Weak events, not visible in the individual seismogram of the network, are missed out. We present an approach, where no picking of events in the seismograms of the recording network is required. The observed wavefield of the network is reversed in time and then considered as the boundary value for the reverse modelling. Assuming the correct velocity model, the reversely modelled wavefield focuses on the hypocentre of the seismic event. The origin time of the event is given by the time where maximum focussing is observed. The spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition. This automatically provides the uncertainty in the localization with respect to the bandwidth of the recorded data. The method is particularly useful for the upcoming large passive networks since no picking is required. It has great potential for localizing very weak events, not detectable in the individual seismogram, since the reverse modelling sums the energy of all recorded traces and, therefore, enhances the signal-to-noise ratio similar to stacking in seismic exploration. The method is demonstrated by 2-D and 3-D numerical case studies, which show the potential of the technique. Events with a S/N ratio smaller than 1 where the events cannot be identified in the individual seismogram of the network are localized very well by the method.

Exploring the potentials and limitations of the time-reversal imaging of finite seismic sources

“…Early applications were limited to structurally simple or acoustic models (e.g. McMechan et al, 1985;Rietbrock and Scherbaum, 1994;Fink, 1996), but recent advances in numerical modelling enabled applications in more complex scenarios with different types of seismic sources, including the classic double couple point source (Gajewski and Tessmer, 2005), extended faults (Ishii et al, 2005;Larmat et al, 2006;Allmann and Shearer, 2007), micro-seismic tremor (Steiner et al, 2008) and volcanic long-period events (O'Brien et al, 2011). Larmat et al (2009) demonstrate the need to use specific imaging fields such as divergence or strain to distinguish sources from low velocity zones.…”

Surface microseismic imaging in the presence of high-velocity lithologic layers

“…The reverse time imaging approach makes use of the reversibility of wave equations to numerically back propagate a recorded seismogram through a known velocity field allowing the energy of a recorded wave to be propagated backwards in time towards its source (e.g., McMechan, 1982;Gajewski & Tessmer, 2004;Xuan & Sava, 2010;Artman et al, 2010;Chambers et al, 2014). Using the concept of the exploding reflector model (e.g., Claerbout, 1982), each time step is considered an equivalent source to the recorded seismogram signal and continued propagation of the wave-field backwards in time will eventually result in the energy being focused at the source location.…”

Time reversal seismic source imaging using peak average power ratio (PAPR) parameter

“…The following were tested as imaging parameters: maximum horizontal and vertical displacement components (Hu and McMechan 1988;Steiner and Saenger 2012;Saenger 2011), maximum particle velocity (Steiner et al 2008), strain components (Blomgren et al 2002), maximum amplitude of pressure value (Gajewski and Tessmer 2005), stress components' energy density (Gajewski and Tessmer 2005; Saenger 2011), maximum P-and S wave energy density, maximum energy density, and maximum stress components (Saenger 2011). With regard to the acoustic wave field modelling, the maximum absolute pressure value (MAPV) applied as an imaging condition appears to be a good indicator of the point source location (Eq.…”

“…The development of theoretical aspects of the method and its application in non-destructive testing were continued by Anderson et al (2009a, b) and Saenger et al (2011). The TRI technique in seismology has been used in source location and identification of source mechanisms (Gajewski and Tessmer 2005;Larmat et al 2006Larmat et al , 2010Kawakatsu and Montagner 2008;Steiner and Saenger 2010;Artman et al 2010;Debski 2015). In seismic exploration the TRI technique has been applied to wave field migration (Baysal et al 1983;McMechan 1983;Tarantola 1988;Fichtner et al 2006) and structure imaging in complex geological conditions like salt domes (Willis et al 2006).…”