On this page you find some selected applications of the method Nanoseismic Monitoring.
Active fault mapping & aftershock monitoring
Seismic aftershock monitoring – Spatiotemporal distribution of aftershocks of the 2004 December 5 ML = 5.4 Waldkirch (Germany) earthquake
The Waldkirch earthquake on 2004 December 5 with ML=5.4 resulted in numerous aftershocks. As a result of the flexibility andportability of the small aperture array, and the independency of anexternal infrastructure like power supply or shelter, we were able to install the small array only 14 hr after the main shock. It enabled the possibility of an intense study of the spatiotemporal behaviour of the aftershocks. The main objective of this paper is to present the results of the data recorded with one small array. During the period of about 39 hr more than 700 events in the magnitude range –1.7≤ ML ≤3.0 were recorded. By contrast, the temporary and permanent seismic network recorded 232 events with ML>0.5 within 313 days after the main shock.
Reference: HÄGE, M. & JOSWIG, M. 2009. Spatiotemporal distribution of aftershocks of the 2004 December 5 ML = 5.4 Waldkirch (Germany) earthquake. Geophysical Journal International, 178, 1523-1532.
Active fault mapping – Spatiotemporal characterization of interswarm period seismicity in West Bohemia
The West Bohemia/Vogtland region is one of the seismically most interesting areas in Europe because of its swarm-like occurrence of seismicity. The installation of the local West Bohemian seismological network (WEBNET) has made the recording of small magnitude seismicity (detection threshold ML ≈ −0.5) possible. We investigated if microseismicity exists below the detection threshold of WEBNET. A microseismic field campaign was carried out in the focal area Nov´y Kostel. The measurement was performed with three small arrays lasting
for 6 d in a seismically quiet, interswarm period. We were able to detect and locate 13 microearthquakes in the magnitude range −1.5 ≤ ML ≤ −0.1 and achieved a detection
threshold about one magnitude lower than the local network. A relative location suggests that the recorded seismicity is rather related to a specific fault segment than randomly distributed. The determined fault zone is aligned NW–SW and confirms the viability of mapping active faults with short-term measurements. The results demonstrate that a linear extrapolation of the b-value, determined by the network bulletin, down to ML =−0.5 fits well with the amount of our recorded events.
Reference: HÄGE, M. & JOSWIG, M. 2009. Spatiotemporal characterisation of interswarm period seismicity in the focal area of Nový Kostel (West-Bohemia/Vogtland) by a short-term microseismic study. Geophysical Journal International, 179, 1071-1079.
Induced Seismicity Monitoring – Combining network and array waveform coherence for automatic location
This study showed how the automatic location for microseismicmonitoring can benefit by integrating the information of small aper-ture arrays into source scanning. Multiple steps from literature arecombined with the new approach of using the Fisher ratio in com-bination with the STA/LTA on the stacked seismograms as the CF for source scanning. Separate stacks for P-andS-onsets with individual velocity models are combined. Horizontal traces are rotated depending on backazimuth and all CFs are normalized. A Gaussian uncertainty window around theoretical onset times is used for stacking with a window size depending on source grid cell location. 3-D velocity models are supported and easy integration of surfacetopography in the models is provided. Considering all steps, the CF becomes strongly dependent on the source location grid cell.
Reference: SICK, B. & JOSWIG, M. 2017. Combining network and array waveform coherence for automatic location: examples from induced seismicity monitoring. Geophys. J.Int.,208(3),1373-1388.
Induced Seismicity Monitoring – EGS hydraulic stimulation monitoring by surface arrays: the Basel Deep Heat Mining Project
The potential and limits of monitoring induced seismicity by surface-based mini arrays was evaluated for the hydraulic stimulation of the Basel Deep Heat Mining Project. This project aimed at the exploitation of geothermal heat from a depth of about 4,630 m. As reference for our results, a network of borehole stations by Geothermal Explorers Ltd. provided ground truth information. We utilized array processing, sonogram event detection and outlier-resistant, graphical jackknife location procedures to compensate for the decrease in signal-to-noise ratio at the surface. We could correctly resolve the NNW–SSE striking fault plane by relative master event locations. Statistical analysis of our catalog data resulted in ML 0.36 as completeness magnitude, but with significant day-to-night dependency. To compare to the performance of borehole data with MW 0.9 as completeness magnitude, we applied two methods for converting ML to MW which raised our MC to MW in the range of 0.99–1.13. Further, the b value for the duration of our measurement was calculated to 1.14 (related to ML), respectively 1.66 (related to M W), but changes over time could not be resolved from the error bars.
Reference: HÄGE, M., BLASCHECK, P. & JOSWIG, M. 2013. EGS hydraulic stimulation monitoring by surface arrays–location accuracy and completeness magnitude: the Basel Deep Heat Mining Project case study,J. Seismol.,17,51–61.
Landslide Monitoring – Analysis of Pre-collapse Failure Signals from a Destructive Rockfall by Nanoseismic Monitoring
A massive rockfall with an estimated volume of approxi-mately 15 000 m3 occurred on 10 May 2011 in the “Rappenlochschlucht” gorge, Vorarlberg, Austria, and destroyed an important massive bridge construction. Using a permanent seismic network at the Heumoes slope in a distance of around 5 km to the “Rappenlochschlucht” gorge, we were able to record the rockfall. Beside the registration of the main rockfall event, we were able to identify two weaker rockfalls which occurred several hours before and whose signals show remarkable similarities to “avalanche” signals. The equivalent magnitude of the main event is estimated to be ML,eq=2.3, while the magnitude of the weaker ones is comparable to ML,eq=0.0.
Reference: WALTER, M., SCHWADERER, U. & JOSWIG, M. 2012. Analysis of Pre-collapse Failure Signals from a Destructive Rockfall by Nanoseismic Monitoring. Nat. Hazards Earth Syst. Sci., 12, 3545–3555.
Landslide Monitoring – Slidequake Generation versus Viscous Creep at Softrock-landslides
By applying passive seismic monitoring approaches at three different creeping softrock landslides, we were able to infer what conditions led to brittle failure,as evident in episodes of slidequakes (down to ML = -2.0) along specific boundaries, and to aseismic creep. At the Slumgullion landslide, the majority of slidequakes occurred at the lateral boundaries of the landslide, while no events were detected along the basal surface. At Heumoes slope, the slidequakes cluster in the slope area with the lowest surface displacement rates. A significant bedrock rise,oriented perpendicular to the direction of slope movement, divides the landslide geometry in two basins, and probably impedes motion, slows the slide, and leads to slidequakes. At the Super-Sauze mudslide, the slidequakes are preferentially generated in its center where the deformation rates are highest. There, the slidequake generation is directly linked to in situ bedrock crests that border several gullies oriented inline with the direction of the entire slope movement.
Reference: WALTER, M., GOMBERG, J., SCHULZ, W., BODIN, P. & JOSWIG, M. 2013. Slidequake Generation versus Viscous Creep at Softrock-landslides: Synopsis of Three Different Scenarios at Slumgullion Landslide, Heumoes Slope, and Super-Sauze Mudslide. Journal of Environmental and Engineering Geophysics 2013; 18 (4): 269–280