In 2020 and 2021 the STIMTEC-X hydraulic stimulation experiment was performed at ca.~130 m below surface at the Reiche Zeche underground research laboratory in Freiberg, Saxony/Germany. The project temporally followed the STIMTEC experiment at the same site and aimed at understanding the stress heterogeneity of the anisotropic and metamorphic gneiss rock mass. The STIMTEC-X experiment applied the hydraulic stimulation technique in several boreholes at the mine-scale. Complementary to the stimulations, there were active seismic ultrasonic transmission data acquired before the stimulations.
We use a seismic monitoring network consisting of six single-component acoustic emission (AE) sensors (sensitivity 1-60 kHz), six hydrophone-like AE sensors (sensitivity 1-40 kHz) and four to twelve single-component Wilcoxon accelerometers (sensitivity 50 Hz-25 kHz). The AE sensors and remained stationary in sub-horizontal and upwards reaching boreholes, the accelerometers were mostly installed along the tunnel walls with one accelerometer in a shallow borehole in each tunnel, and the hydrophone-like AE sensors were installed in the down-going water filled boreholes, but repositioned for each measurement campaign (Figure 1).
This data set of 120 active ultrasonic transmission (UT) measurements is supplementary to Boese et al. (2022, in review), which introduces some of the active measurement campaigns of the STIMTEC-X experiment in detail. The whole data set togetter with the “Ultrasonic transmission measurements from six boreholes from the STIMTEC experiment, Reiche Zeche Mine, Freiberg (Saxony, Germany)” [https://doi.org/10.5880/GFZ.4.2.2021.002] was used to evaluate performance measures such as sensitivity and frequency bandwith, coupling, placement and polarity of the hydrophone-like AE sensor compared to AE sensors. The active seismic data provided here are from seven boreholes (BH01, BH05, BH06, BH10, BH14, BH18, BH19) as shown in Figure 1.
There are nine tables provided as metadata of which seven contain the STIMTEC-X sensor coordinates for each measurement campaign, the event information of all the 120 UT measurements and the UT picks. The UT measurements were recorded with a sampling rate of 1 MHz and results from an automatic stack of 1024 UT pulses generated by the ultrasonic transmitter and recorded by the STIMTEC-X sensors.
The UT measurements are saved in binary file format (fsf file format). Fsf-files can be processed with FOCI software: https://www.induced.pl/software/foci. Each fsf file contains 32768 samples, which corresponds to 0.032768 seconds. All UT event files were manual inspected and phase arrivals identified. These are stored in the fsf-file header as well as in the table STIMTECX_UT_picks.csv.
Between early 2018 and late 2019 the STIMTEC hydraulic stimulation experiment was performed at ca.~130 m below surface at the Reiche Zeche underground research laboratory in Freiberg, Saxony/Germany. The project aimed at gaining insight into the creation and growth of fractures in anisotropic and heterogeneous metamorphic gneiss , to develop and optimise hydraulic stimulation techniques and to control the associated induced seismicity under in situ conditions at the mine-scale. These aspects of failure and associated seismicity are important for the development of enhanced geothermal energy systems.
A combined seismic network consisted of 12 single-component acoustic emission sensors (sensitivity 1-100 kHz) and three single-component Wilcoxon accelerometers (sensitivity 50 Hz-25 kHz) were installed in boreholes drilled into the test volume, surrounding the stimulation site (Figure 1). A stimulation borehole with 63 m length was drilled with 15° northward inclination.
This data set of 314 active ultrasonic transmission (UT) measurements is supplementary to Boese et al. (2021, in review), which introduces the STIMTEC experiment and its active measurement campaigns. This data set was used to derive an anisotropic velocity model for the STIMTEC rock volume. The active seismic data provided here are from six boreholes (BH09, BH10, BH12, BH15, BH16, BH17) as shown in Figure 1. of the associated data description.
There are three tables provided as metadata that contain the STIMTEC sensor coordinates, event information of the 314 UT measurements and the UT picks. The UT measurements were recorded with a sampling rate of 1 MHz and results from an automatic stack of 1024 UT pulses generated by the ultrasonic transmitter and recorded by the STIMTEC sensors.
The UT measurements are saved in binary file format (fsf file format). Fsf-files can be processed with FOCI software: https://www.induced.pl/software/foci
Each fsf file contains 32768 samples, which corresponds to 0.032768 seconds. All UT event files were manual inspected and phase arrivals identified. These are stored in the fsf-file header as well as in the table STIMTEC_UT_picks.csv.
The Black Forest Observatory Data collection compiles digital data recorded at Black Forest Observatory (BFO) in Germany and provided through several international data centers. BFO aims to observe the entire geodynamic spectrum. It strives to ensure continuous, uninterrupted operation and is internationally recognized for high signal quality and sensitivity. Observed quantities cover three components of acceleration (including ground motion, gravity and tilt), strain, magnetic field, and others (see description of instruments below). The set of instruments and data recorders in operation provides a significant level of redundancy, which allows to distinguish natural phenomena from possible instrumental artefacts.
The Black Forest Observatory (BFO) is a joint research facility of the Karlsruhe Institute of Technology (KIT) and the University of Stuttgart (Duffner et al., 2018; Gottschämmer et al. 2014). Since 1971 it is operated in cooperation of the geophysical and geodetic institutes of both universities (Zürn, 2014). BFO is staffed with two scientists and one technician. Main activities of the observatory fall into four categories, which are (1) observation and publication of a continuously recorded multi-parameter geodynamic data set, (2) research, (3) hosting of guest-experiments, and (4) teaching.
The location of the observatory (48.3301 °N, 8.3296 °E) in the middle of the Black Forest was carefully selected at large distances to potential anthropogenic sources of noise. The instruments are deployed in a former silver mine in competent granite rock at a depth of up to 170 m below the surface and at up to 700 m distance from the entrance of the mine. This provides a thermally very stable environment. Two air-locks provide additional protection against air-pressure variations and ensure thermal stability. Because of these favorable conditions and the excellent high precision instruments operated at BFO the observatory is internationally well known as one of the most sensitive sites for long period observations, providing international standards for the scientific community, e.g. for recordings of Earth's free oscillations.
The Black Forest Observatory operates broad-band seismometers (STS-1 and STS-2), gravimeters (superconducting gravimeter SG056, LaCoste Romberg earth-tide gravimeter ET-19), tiltmeters (Askania borehole tiltmeter, Horsfall fluid tiltmeter), an array of three invar-wire strainmeters, magnetometers (a scalar GSM-90 Overhauser magnetometer and a three component Rasmussen fluxgate magnetometers) and a permanent GPS-station. These are supplemented by regularly repeated magnetic base-line measurements and observations of absolute gravity as well as the recording of several environmental parameters (air-pressure, infrasound, humidity, wind speed, precipitation and temperature). Some of the latter are used to correct geodynamic recordings for remaining disturbances.
The data are published in near-real-time through international data centers (IRIS DMC at Seattle, SZO at the BGR in Hannover, INTERMAGNET, GNSS Data Center at the BKG in Frankfurt, IGETS Database at GFZ Potsdam). Data are made available free of charge to scientific projects as well as to the general public with attribution as defined in the Creative Commons Attribution 4.0 International Licence (CC BY 4.0).
An extended review of research at BFO is given by Zürn (2014) and Duffner et al. (2018, in German). Both provide references to published BFO research.