Monitoring the West Bohemian earthquake swarm in 2008/2009 by a temporary small-aperture seismic array

Abstract

The most recent intense earthquake swarm in West Bohemia lasted from 6 October 2008 to January 2009. Starting 12 days after the onset, the University of Potsdam monitored the swarm by a temporary small-aperture seismic array at 10 km epicentral distance. The purpose of the installation was a complete monitoring of the swarm including micro-earthquakes (M L < 0). We identify earthquakes using a conventional shortterm average/long-term average trigger combined with sliding-window frequency-wavenumber and polarisation analyses. The resulting earthquake catalogue consists of 14,530 earthquakes between nitudes in the range of −1.2 ≤ M L ≤ 2.7. The small-aperture seismic array substantially lowers the detection threshold to about M c = −0.4, when compared to the regional networks operating in West Bohemia (M c > 0.0). In the course of this work, the main temporal features (frequencymagnitude distribution, propagation of back azimuth and horizontal slowness, occurrence rate of aftershock sequences and interevent-time distribution) of the recent 2008/2009 earthquake swarm are presented and discussed. Temporal changes of the coefficient of variation (based on interevent times) suggest that the swarm earthquake activity of the 2008/2009 swarm terminates by 12 January 2009. During the main phase in our studied swarm period after 19 October, the b value of the Gutenberg-Richter relation decreases from 1.2 to 0.8. This trend is also reflected in the powerlaw behavior of the seismic moment release. The corresponding total seismic moment release of 1.02 × 10 17 Nm is equivalent to M L,max = 5.4.

Aseismic transient driving the swarm-like seismic sequence in the Pollino range, Southern Italy

“…6); only for phase 0 we cannot reject at 5 per cent confidence level the null hypothesis of exponentially distributed interevent times. This is similar to fractal temporal clustering found for example for the 2000 and 2008 Vogtland swarms (Hainzl & Fischer 2002;Hainzl et al 2012;Hiemer et al 2012). There, a similar degree of dispersion of interevent times has been interpreted as a common triggering mechanisms across all sequences (Hainzl & Fischer 2002).…”

“…The observation of decreasing b-values correlated with an increasing rate of seismicity seems to be a common characteristic of some tectonic swarms (Hainzl & Fischer 2002;Hiemer et al 2012) although the physical mechanisms behind this is still unclear. of events (i.e.…”

“…Exponential distributed variables have CV = 1 while overdispersed data take CV > 1 indicating a degree of clustering in time usually described well with a power-law behaviour. Swarm-like sequences are expected to have a high degree of clustering (CV > 1) and interevent times show selfsimilarity in a time scale from minutes to days (Hainzl & Fischer 2002;Hiemer et al 2012;Hainzl et al 2012).…”

Determination of 0 and Rock Site from Records of the 2008/2009 Earthquake Swarm in Western Bohemia

“…The swarm earthquake catalog contains 14,530 earthquakes in the local magnitude range of -1.2 ≤ M L ≤ 2.7 ( Figure 2) including eight M L ≥ 2.6 earthquakes (Hiemer et al 2010). The highest number of events was detected at magnitudes around M L = -0.5 (histogram in Figure 2).…”

Seismotectonic significance of the 2008–2010 Walloon Brabant seismic swarm in the Brabant Massif, Belgium

“…In an intraplate continental tectonic setting, seismic swarms are commonly associated with stress perturbations caused by magmatic intrusions, volcanic activity and with gradual fluid transport in the seismogenic part of the crust (Hainzl, 2004;Hiemer et al, 2012;Schenk et al, 2012;Špičák, 2000). In volcanic areas, continental rift and subduction zones, large fluid-and gas movements such as CO 2 release along prominent faults or fault intersections can generate earthquake swarms (e.g.…”