Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Seismic source inversion in mining environments Simone Cesca Institute of Geophysics, University of Hamburg

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Outline The MINE project background, structure and project aims Seismic source inversion problem theory and methods point and kinematic source inversion using the Kiwi tools Source inversion in mining environments an application to coal mining induced seismicity (Ruhr, Germany)

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha The MINE project, a quick overview MINing Environment: continuous monitoring and simultaneous inversion Funding, positions, timeline German Ministery of Education and Science (BMBF – Geotechnologien Programme) Junior Research project, 1 Leading Scientist + 3 PhDs 3+3 years duration (started ) Aims Mining monitoring (seismicity, fracturing, stress perturbation) and imaging Adapt full waveform techniques from classical seismology and to mining Combine information from different data streams Provide portable software tools to analyse mine datasets

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Research lines Detection and location using full waveforms Signal characterization Moment tensor inversion Extended source parameters Spatio-temporal patterns of seismicity Stress inversion (seismicity patterns and focal mechanisms) Local earthquake tomography WP1 Detection, Location, Characterization WP3 Stress inversion WP2 Source Inversion WP4 Tomography

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Hamm, Ruhr region Courtesy M. Bischoff Biscoff et al. (2010)

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Pyhäsalmi Deep metal mine in Europe Collaboration with NORSAR (Kuhn, Oye, Roth, Nath) 3D velocity model Multi-stream monitoring system Seismic Internal deformation Thermal measurements Others Figure T. Mäki (2000)

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Cerville SALT MARLS LIMESTONE (DOLOMIE) 190 m 125 m 50 m Courtesy P. Jousset

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Source inversion in seismology

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Source inversion in seismology, overview Global CMT catalogue, shallow earthquakes, Slip map kinematic model (Li et al. 2002) Source:

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Source inversion in seismology, what do we need? Moment tensor / Kinematic source Inversion routine Plotting and result evaluation Data access (waveform and metadata) Data preprocessing Green's functions (database) Inversion method, Inv. Parameters (e.g. BP, tapers,...)

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha OpenSource Running under Linux Python + Fortran implementation Source inversion in seismology using the Kiwi tools

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Point source model, double couple & moment tensor More complete point source model is represented by a moment tensor (MT) MT = MT DC + MT CLVD + MT ISO Earthquakes is often well modeled in terms of shear cracks, using a point source representation (DC model). after Hasegawa et al. (1989)

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Extended source model, definitions Extended sources may be reproduced by superposition of several point sources distributed along a planar (or bended) rupture surface. Each point source start radiating when reached by the rupture front. Radiation lasts for a given (rise) time.

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha The eikonal source model Circular area, plus constraints Rupture velocity scales with shear velocity Despite its flexibility, the eikonal source model is described by only 13 parameters (considering constraints and earth model as fixed and known)

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha One earthquake, five solutions

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Source model parameters and inversion priorities Source model parameters (13) TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad General source description Source locationRadiation patternRupture process Scale of source model Point sourceFinite source Information from data Low frequenciesHigh frequencies Inversion priority Step 1, 2Step 3

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Greece, Shallow earthquakes extended sources Cesca et al. JGR 2010

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Source inversion, natural and induced seismicity Cesca et al. submitted

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Source inversion in mining environment

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Bischoff et al Ruhr region Coal mining induced seismicity monitored by Ruhr University since 1983 About 1000 events are recorded between 0.7<ML<3.3 every year Hamm region (blue circle) >7000 events in (14 months) 913 events 0.0<ML<2.0 DC inversion MT inversion Kinematic inversion and rupture modeling

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Seismicity follows longwall mining, Epicenters are spreaded over an area of about 2x2km 6 broadband stations (5 Guralp CMG, pink; 1 Trillium 40, purple) 9 short-period (Mark L-4C-3D, orange) 3 subsurface stations (yellow) We work here at 0.5-2Hz or 1-4Hz, only BB stations are used

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Seismicity follows longwall mining Additional clusters Average depth above mining level Bimodal frequency-magnitude distribution

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Inversion strategy DepthM0M0 StrikeDipRake TimeLatLon TimeLatLonNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRadTimeLatLon DepthM0M0 Step 1, Focal mechanism (DC and full moment tensor) amplitude spectra inversion, whole waveform DepthM0M0 StrikeDipRake 1

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Inversion strategy DepthM0M0 StrikeDipRake TimeLatLon TimeLatLonNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRadTimeLatLon DepthM0M0 Step 1, Focal mechanism (DC and full moment tensor) amplitude spectra inversion, whole waveform DepthM0M0 StrikeDipRake 1 Step 2, Polarity control / Centroid location time domain inversion, whole waveforms DepthM0M0 StrikeDipRake TimeLatLon 2

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Inversion strategy DepthM0M0 StrikeDipRake TimeLatLon TimeLatLonNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRakeNucXNucYRuptVRiseTRadTimeLatLon DepthM0M0 Step 1, Focal mechanism (DC and full moment tensor) amplitude spectra inversion, whole waveform DepthM0M0 StrikeDipRake 1 Step 2, Polarity control / Centroid location time domain inversion, whole waveforms DepthM0M0 StrikeDipRake TimeLatLon 2 Step 3, Kinematic model amplitude spectra or time domain inversion, including high freqencies NucXNucYRuptVRiseTRad TimeLatLonDepthM0M0 StrikeDipRake 3

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha DC inversion results overview Successful inversion for 578 (over 913) Magnitude range, Mw Very similar mechanisms Normal faults (80%) or oblique-normal One steep plane, one sub-horizontal Different strike are observed, strike angles are related to mining geometry

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Wehling-Benatelli (2011) Courtesy D. Becker Waveform similarity analysis and cluster analysis (relocated events) Consistent focal mechanisms for Major clusters

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Moment tensor / extended source parameters Full MT solutions significant for more than 100 events Non-DC terms results are still ambiguous Possible inversion artefact rather than source features Preliminar kinematic inversion for 24 largest events (Ml > 1.0) Kinematic model is significant for 8 events, only In almost all cases (7), the vertical rupture plane is preferred

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Conclusions Full waveform moment tensor inversion successfully applied to mining induced seismicity at local scale (<2km) for low magnitude events (at now, down to Mw 0.3). DC and MT focal mechanisms were successfully obtained for 587 selected events Results are in good agreement with reference, when available (about 100 events), based on first polarities and S wave polarization. Better results are obtained for a layered model and frequency range 0.5-2Hz Focal mechanisms are characterized by similar ruptures. Normal faulting with one steep fault plane. In general, striking angles are linked to the mining geometry. Non-DC resolution to be judged Preliminar kinematic modeling for largest events (Ml≥1.0) point to a similar rupture mechanism along sub-vertical planes.

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Thanks to: A. T. Şen, Prof. Dr. T. Dahm, Dr. S. Heimann, F. Grigoli, S. Maghsoudi, A. Rohr, M. Bischoff, T. Meier, S. Wehling-Benatelli BMBF project MINE GEOTECHNOLGIEN programme The Kiwi tools are currently used at: University of Hamburg, University of Potsdam, BGR Hannover, GFZ Potsdam, University of Coimbra, Aristotle University of Thessaloniki,Ruhr University Bochum Further info on software and applications: Cesca et al., JGR 2010 Cesca et al., J. Seismol Cesca et al., J. Seismol., submitted

Cesca, Source inversion in mining environments AIM 2 nd annual meeting, , Institute of Geophysics, Academy of Sciences of the Czech Republic, Praha Thanks for your attention