Seismicity patterns and variation of the frequency-magnitude distribution of microcracks in salt

Köhler, Nina; Spies, Thomas; Dahm, Torsten

doi:10.1111/j.1365-246x.2009.04303.x

Cited by 18 publications

(16 citation statements)

References 16 publications

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“…Magnitudes of AE data (M AE ) were calculated from the recorded amplitudes and corresponding source-receiver distances. They are reported in decibels at a reference epicentral distance (Köhler et al, 2009). M AE values of this catalog were arbitrarily scaled by a factor of 0.05 to range between 0 and 5, which could correspond to M w from −8 to −3, according to empirical energy relations (Eisenblätter and Spies, 2000;Kaiser, 2011).…”

Section: Datamentioning

confidence: 99%

Maximum Magnitude of Completeness in a Salt Mine

Maghsoudi¹,

Cesca²,

Hainzl³

et al. 2015

Bulletin of the Seismological Society of America

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In this study, we analyze acoustic emission (AE) data recorded at the Morsleben salt mine, Germany, to assess the catalog completeness, which plays an important role in any seismicity analysis. We introduce the new concept of a magnitude completeness interval consisting of a maximum magnitude of completeness (M cmax ) in addition to the well-known minimum magnitude of completeness. This is required to describe the completeness of the catalog, both for the smallest events (for which the detection performance may be low) and for the largest ones (which may be missed because of sensors saturation). We suggest a method to compute the maximum magnitude of completeness and calculate it for a spatial grid based on (1) the prior estimation of saturation magnitude at each sensor, (2) the correction of the detection probability function at each sensor, including a drop in the detection performance when it saturates, and (3) the combination of detection probabilities of all sensors to obtain the network detection performance. The method is tested using about 130,000 AE events recorded in a period of five weeks, with sources confined within a small depth interval, and an example of the spatial distribution of M cmax is derived. The comparison between the spatial distribution of M cmax and of the maximum possible magnitude (M max ), which is here derived using a recently introduced Bayesian approach, indicates that M max exceeds M cmax in some parts of the mine. This suggests that some large and important events may be missed in the catalog, which could lead to a bias in the hazard evaluation.

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Section: Datamentioning

confidence: 99%

Maximum Magnitude of Completeness in a Salt Mine

Maghsoudi¹,

Cesca²,

Hainzl³

et al. 2015

Bulletin of the Seismological Society of America

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“…AE events in the mine are located automatically with a triggering approach, and only event parameters such as hypocenter, origin time, automatically determined P-and S-wave onsets, and maximum amplitude are saved in a log file. (The waveforms are not routinely retained; see Spies and Eisenblätter, 2001, Köhler et al, 2009, and Becker et al, 2010, for specifics of the recording system and the localization procedure.) Data are sampled with 200 kHz, and the main signal energy is in the 1-20 kHz frequency range.…”

Section: Study Site and Monitoring Networkmentioning

confidence: 99%

“…1), which results in a slightly reduced magnitude range of the AE catalog when compared to the center of the AE network. Nevertheless, the location accuracy for welllocated AE events is on the order of 1-2 m (Becker et al, 2010), and the number of events recorded in the vicinity of the cavity is high enough for a detailed analysis of microcracking processes in this area (Köhler et al, 2009;Becker et al, 2010).…”

Section: Study Site and Monitoring Networkmentioning

confidence: 99%

Macroscopic Failure Processes at Mines Revealed by Acoustic Emission (AE) Monitoring

Cailleau¹,

Kaiser²,

Dahm³

2014

Bulletin of the Seismological Society of America

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Mining activity may cause different types of seismicity and rock failure.Typical events include (1) fully induced microearthquakes in close proximity to galleries and human activity due to high-stress concentrations (border fractures) and (2) triggered earthquakes within the rock mass at larger distance to the source of the stress perturbation (inner fractures). Type 1 is important to understand the development of rock bursts and evaluate the stability of the mine. Type 2 may be associated with larger events releasing pre-existing stress and being triggered by stress changes due to the mining operation. They are important to assess the seismic hazard related to mining activity.To analyze these different failure processes, we use a dataset of high-frequency acoustic emission (AE) events monitored in an abandoned salt mine. The process of fracture formation in the rock mass was enhanced by the backfilling of a cavity. Thermal stresses induced by the backfilling operation are modeled with a finite-element approach, and observed AE activity is used to quantify the mechanism of event triggering in terms of a Coulomb failure model.Two observations are outstanding. First, the instantaneous triggering of enhanced activity and the slow growth of an inner fracture in relatively far distance to the backfilled cavity is detected. The structure already showed AE activity before the refilling started and was triggered by traction-like stress transfer. Its AE activity correlates well with the calculated Coulomb stress changes at the beginning of backfilling. Second, the sudden occurrence of a macroscopic, induced border fracture at the backfilled gallery which is oriented in agreement with the acting stress field is observed. Although AE activity at the inner fracture was triggered by tiny Coulomb stress changes, indicating a structure already in critical state, formation of the border fracture required significantly larger stresses, hinting at a previously intact rock volume.Online Material: Figure depicting the variability of the static Coulomb stress changes on the inner fracture for different rake values.

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“…Amitrano, 2003) and possibly also the material involved in the failure process (e.g. Köhler et al, 2009). Furthermore, it is well known that FMDs in the mining environment often exhibit a bimodal character (e.g.…”

Section: Frequency Magnitude Distributionsmentioning

confidence: 99%

Indications for different types of brittle failure due to active coal mining using waveform similarities of induced seismic events

et al. 2013

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Abstract. Longwall mining activity in the Ruhr coal mining district leads to mining-induced seismicity. For detailed studies the seismicity of a single longwall panel beneath the town of Hamm-Herringen in the eastern Ruhr area was monitored between June 2006 and July 2007 with a dense temporary network of 15 seismic stations. More than 7000 seismic events with magnitudes between −1.7 ≤ M L ≤ 2.0 were detected and localized in this period. Most of the events occurred in the vicinity of the moving longwall face.In order to find possible differences in the brittle failure types of these events an association of the events to distinct clusters is performed based on their waveform characteristics. This task is carried out using a new clustering algorithm utilizing a network similarity matrix which is created by combining all available 3-component single station similarity matrices. The resultant network matrix is then sorted with respect to the similarity of its rows leading to a sorted matrix immediately indicating the clustering of the event catalogue. Finally, clusters of similar events are extracted by visual inspection.This approach results in the identification of several large clusters which are distinct with respect to their spatial and temporal characteristics as well as their frequency magnitude distributions. Comparable clusters are also found with a conventional single linkage approach, however, the new routine seems to be able to associate more events to specific clusters without merging the clusters.The nine largest observed clusters can be tentatively divided into three different groups that indicate different types of brittle failure. The first group consists of the two largest clusters which constitute more than half of all recorded events. Results of a relative relocation using cross-correlation data suggest that these events are confined to the extent of the mined out longwall and cluster close to the edges of the active longwall at the depth of active mining. These events occur in lockstep with the longwall advance and exhibit a high b value of the Gutenberg-Richter relation (GR) of about 1.5 to 2.5 and consist of small magnitude events. Thus, these events represent the immediate energy release adjacent to the mined out area.The second group consists of clusters located either slightly above or below the depth of active mining and occurring at the current position of the longwall face within the confines of the longwall. They consist of generally stronger events and do not follow GR. This activity might be linked to the failure of more competent layers above and below the mined out seam resulting in larger magnitude events.Finally, one cluster represents seismic activity with a rather low b value below 1 and events located partly towards the north of the longwall which are delayed with respect to the advance of the longwall face. These events are interpreted as brittle failure on pre-existing tectonic structures reactivated by the mining activity.Published by Copernicus Publications on behalf of t...

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Seismicity patterns and variation of the frequency-magnitude distribution of microcracks in salt

Cited by 18 publications

References 16 publications

Maximum Magnitude of Completeness in a Salt Mine

Maximum Magnitude of Completeness in a Salt Mine

Macroscopic Failure Processes at Mines Revealed by Acoustic Emission (AE) Monitoring

Indications for different types of brittle failure due to active coal mining using waveform similarities of induced seismic events

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