TY  - CONF
ID  - epos1991
UR  - http://meetingorganizer.copernicus.org/EGU2017/EGU2017-1875.pdf
A1  - Lopez-Comino, Jose Angel
A1  - Cesca, Simone
A1  - Heimann, Sebastian
A1  - Grigoli, Francesco
A1  - Milkereit, Claus
A1  - Dahm, Torsten
A1  - Zang, Arno
Y1  - 2017/04//
N2  - A crucial issue to analyse the induced seismicity for hydraulic fracturing is the detection and location of massive
microseismic or acoustic emissions (AE) activity, with robust and suf?ciently accurate automatic algorithms.
Waveform stacking and coherence analysis have been tested for local seismic monitoring and mining induced
seismicity improving the classical detection and location methods (e.g. short-term-average/long-term-average and
automatic picking of the P and S waves ?rst arrivals). These techniques are here applied using a full waveform
approach for a hydraulic fracturing experiment (Nova project 54-14-1) that took place 410 m below surface in the
Äspö Hard Rock Laboratory (Sweden). Continuous waveform recording with a near ?eld network composed by
eleven AE sensors are processed. The piezoelectric sensors have their highest sensitive in the frequency range 1
to 100 kHz, but sampling rates were extended to 1 MHz. We present the results obtained during the conventional,
continuous water-injection experiment HF2 (Hydraulic Fracture 2). The event detector is based on the stacking
of characteristic functions. It follows a delay-and-stack approach, where the likelihood of the hypocenter location
in a pre-selected seismogenic volume is mapped by assessing the coherence of the P onset times at different
stations. A low detector threshold is chosen, in order not to loose weaker events. This approach also increases
the number of false detections. Therefore, the dataset has been revised manually, and detected events classi?ed
in terms of true AE events related to the fracturing process, electronic noise related to 50 Hz overtones, long
period and other signals. The location of the AE events is further re?ned using a more accurate waveform stacking
method which uses both P and S phases. A 3D grid is generated around the hydraulic fracturing volume and
we retrieve a multidimensional matrix, whose absolute maximum corresponds to the spatial coordinates of the
seismic event. The relative location accuracy is improved using a master event approach to correct for travel time
perturbations. The master event is selected based on a good signal to noise ratio leading to a robust location with
small uncertainties. Relative magnitudes are ?nally estimated upon the decay of the maximal recorded amplitude
from the AE location. The resulting catalogue is composed of more than 4000 AEs. Their hypocenters are spatially
clustered in a planar region, resembling the main fracture plane; its orientation and size are estimated from the
spatial distribution of AEs.

This work is funded by the EU H2020 SHEER project. Nova project 54-14-1 was ?nancially supported by
the GFZ German Research Center for Geosciences (75%), the KIT Karlsruhe Institute of Technology (15%) and
the Nova Center for University Studies, Research and Development (10%). An additional in-kind contribution of
SKB for using Äspö Hard Rock Laboratory as test site for geothermal research is greatly acknowledged.
TI  - Full waveform approach for the automatic detection and location of
acoustic emissions from hydraulic fracturing at Äspö (Sweden)
M2  - Vienna, Austria
AV  - public
T2  - EGU General Assembly 2017
ER  -