Bernard Dost

Developing an Application‐Specific Ground‐Motion Model for Induced Seismicity

Abstract A key element of quantifying both the hazard and risk due to induced earthquakes is a suite of appropriate ground‐motion prediction equations (GMPEs) that encompass the possible shaking levels due to such events. Induced earthquakes are likely to be of smaller magnitude and shallower focal depth than the tectonic earthquakes for which most GMPEs are derived. Furthermore, whereas GMPEs for moderate‐to‐large magnitude earthquakes are usually derived to be transportable to different locations and applications, taking advantage of the limited regional dependence observed for such events, the characteristics of induced earthquakes warrant the development of application‐specific models. A preliminary ground‐motion model for induced seismicity in the Groningen gas field in The Netherlands is presented as an illustration of a possible approach to the development of these equations. The GMPE is calibrated to local recordings of small‐magnitude events and captures the epistemic uncertainty in the extrapolation to larger magnitude considered in the assessment of the resulting hazard and risk.

Current challenges in monitoring, discrimination, and management of induced seismicity related to underground industrial activities: A European perspective

Due to the deep socioeconomic implications, induced seismicity is a timely and increasingly relevant topic of interest for the general public. Cases of induced seismicity have a global distribution and involve a large number of industrial operations, with many documented cases from as far back to the beginning of the twentieth century. However, the sparse and fragmented documentation available makes it difficult to have a clear picture on our understanding of the physical phenomenon and consequently in our ability to mitigate the risk associated with induced seismicity. This review presents a unified and concise summary of the still open questions related to monitoring, discrimination, and management of induced seismicity in the European context and, when possible, provides potential answers. We further discuss selected critical European cases of induced seismicity, which led to the suspension or reduction of the related industrial activities.

Framework for a Ground-Motion Model for Induced Seismic Hazard and Risk Analysis in the Groningen Gas Field, The Netherlands

The potential for building damage and personal injury due to induced earthquakes in the Groningen gas field is being modeled in order to inform risk management decisions. To facilitate the quantitative estimation of the induced seismic hazard and risk, a ground motion prediction model has been developed for response spectral accelerations and duration due to these earthquakes that originate within the reservoir at 3 km depth. The model is consistent with the motions recorded from small-magnitude events and captures the epistemic uncertainty associated with extrapolation to larger magnitudes. In order to reflect the conditions in the field, the model first predicts accelerations at a rock horizon some 800 m below the surface and then convolves these motions with frequency-dependent nonlinear amplification factors assigned to zones across the study area. The variability of the ground motions is modeled in all of its constituent parts at the rock and surface levels.

Recommendation for the discrimination of human-related and natural seismicity

Various techniques are utilized by the seismological community, extractive industries, energy and geoengineering companies to identify earthquake nucleation processes in close proximity to engineering operation points. These operations may comprise fluid extraction or injections, artificial water reservoir impoundments, open pit and deep mining, deep geothermal power generations or carbon sequestration. In this letter to the editor, we outline several lines of investigation that we suggest to follow to address the discrimination problem between natural seismicity and seismic events induced or triggered by geoengineering activities. These suggestions have been developed by a group of experts during several meetings and workshops, and we feel that their publication as a summary report is helpful for the geoscientific community. Specific investigation procedures and discrimination approaches, on which our recommendations are based, are also published in this Special Issue (SI) of Journal of Seismology.

Implications of salt-related propagation and mode conversion effects on the analysis of induced seismicity

A number of natural gas fields in the north of the Netherlands show moderate seismicity induced by gas extraction. The gas reservoirs are located underneath a thick layer of Zechstein evaporites (salt). The presence of the salt has two important effects on the wave motions of induced events as recorded at the surface close to the epicenter. The first effect is the defocusing of seismic energy, with its implications on observed amplitudes and radiation patterns. The second effect is the relatively strong conversion from P- to S-energy at the bottom of the salt, leading to the presence of S-wave precursors. Failure to recognize these effects may lead to misinterpretation of source location and mechanism. Moreover, the S-wave precursors provide a handle to reduce uncertainty in depth estimation. We investigate the effects using moment tensor inversion and ray tracing for four recent events (ML = 2.6 − 3.5) in the Groningen field.

Setting up a virtual broadband seismograph network across Europe

European seismological observatories have undergone an impressive evolution in the last 5 to 10 years. The result is a very dense, but patch-like coverage, with seismic instruments operated by a multitude of different observatories. Providing the research community with easy and rapid access to all of these waveform data poses a significant challenge. An ongoing European Community-funded project, Mediterranean-European Rapid Earthquake Data Information and Archiving Network (MEREDIAN), aims to shape these national efforts into a European-Mediterranean infrastructure for broadband waveform data exchange and archiving.

Preface to the special issue "Triggered and induced seismicity: probabilities and discrimination"

Triggered and induced seismicity are the earth response to transient non-tectonic phenomena. In a common definition, a triggered earthquake is assumed as an event whose occurrence is anticipated in view of the background seismicity rate. The triggering process, caused by a transient phenomena, only concerns the nucleation of a small region of the rupture area, whereas the entire rupture is controlled by the background stress. An induced event, in change, is entirely (e.g. in terms of rupture size and energy released) controlled by its causative origin and would not occur without it. A complementary, stress-based approach to define the boundary among triggered and induced seismicity was discussed by McGarr and Simpson (1997), in the specific framework of anthropogenic seismicity. According to their classification, a broader term of “stimulated” seismicity could be used to describe both triggered and induced seismicity. Transients which can induce or trigger seismicity can either be of natural or anthropogenic origin. Natural phenomena which can favour seismicity include rain, snow, pore pressure changes, magma dikes, and geothermal and volcanic processes. Earthquake– earthquake interactions may also be considered as a specific case of triggered seismicity. A second, important group of induced and triggered events are those of anthropogenic origin. Different human-related activities may favour, or inhibit, the earthquake occurrence, e.g. by inducing local stress perturbations, affecting the subsurface strain, or inducing changes in the pore pressure. Known cases of human operations which can induce seismicity or microseismicity include mining operations and mass shifts, water reservoir impoundment, drilling, oiland gas-field exploitation, hydro-fracturing, and fluid injection and removal. The theme of induced seismicity, and more specifically of anthropogenic induced seismicity, is nowadays of great interest, not only for the scientific community, but also for the society. On one side, several new techniques have been developed and applied for the purpose of mining, hydrocarbon production, hydraulic fracturing or fluid injection/removal. Related geo-engineering operations can possibly significantly modify the seismicity rate, either inducing or inhibiting the seismicity at different scales. A J Seismol (2013) 17:1–4 DOI 10.1007/s10950-012-9338-z

Intrinsic absorption and scattering attenuation in the southern part of the Netherlands

We present the first systematic study of attenuation derived from the S-wave coda in the frequency range 1-32 Hz for the southern part of the Netherlands and its surroundings. For this we used two methods, the codaQ (Qc) method and the Multiple Lapse Time Window (MLTW) method. In the interpretation of the results both single and multiple scattering in a half space are considered. Our aim is to validate these interpretations in our region and to try to identify theeffects of attenuation due to intrinsic absoprtion (Qi)and scattering attenuation (Qs). For this we analyzedmore than 100 3-component high-quality digital seismograms from 43 crustalevents and 23 different stations in the Netherlands, Germany and Belgium.Coda Q results show smaller Qc (=Q0fn) values for epicentral distances shorter than 25 km (Q0=90) compared to larger epicentral distances (Q0=190), but similar frequency dependence (∝f-0.9). Interpretation of MLTW results provided a seismic albedo smaller then 0.5, suggesting that the intrinsic absorption dominates over scattering in this region. Both Qi and Qs show similar frequency dependences as Qc. These results are comparable to those obtained in other areas, but we also show that more sophisticated models are required to remove ambiguities in the interpretation. For short lapse times and shortevent-station distances we find for the simple half space model a correspondinginterpretation of both methodologies, where Qc correspondsto Qt, suggesting that a model with single scattering in ahalf space is appropriate. For long lapse times and long event station distances, however, we find that the S-wave coda is, most probably, too much influenced by crust-mantel heterogenities and more sophisticated Qinversion models using larger data sets are required for more reliable attenuation estimates.

Comparing Waveforms by Digitization and Simulation of Waveforms for Four Parkfield Earthquakes Observed in Station dbn, The Netherlands

Waveforms from the 2004 Parkfield earthquake are compared with three earlier events in 1922, 1934, and 1966, all recorded in station dbn, The Netherlands, at 80° epicentral distance. Digitization of analog records and simulation of digital data enabled the correlation of surface waves for all events. Normalized correlation values are greater than 0.8 for the Parkfield events themselves, compared to values less than 0.5 for correlation with other events in the same region, either with a different mechanism at close distances (1983 Coalinga and 2003 San Simeon) or with the same mechanism, but at larger distances along the same fault system (1984 Morgan Hill). We find that waveforms from sources with the same mechanism show the highest correlations. Waveform amplitudes of the Parkfield events are similar within the accuracy of the calibration of the instrumentation.

A Shallow Seismic Velocity Model for the Groningen Area in the Netherlands

The province of Groningen in the Netherlands holds one of the worlds largest natural gas fields, and it has been an important source of energy for Western Europe for many decades. The seismicity in recent years called for a better understanding of the local subsurface, and therefore a dense network of 70 boreholes was installed in early 2015. Each borehole is equipped with four geophones and a surface accelerometer. In this study, data from this network are used to determine the shallow velocity structure that is important for the quantification of the seismic hazard and accurate source localizations. Compressional and shear wave velocity profiles with uncertainties are derived for each of the 200 m deep boreholes using passive seismic interferometry applied to local event data. The resulting seismic velocity distributions are presented as contour maps for 50 m depth intervals. The maps show strong lateral variations, where areas of low VP/VS ratio correspond to regions of sedimentary infill. The shear wave velocities were derived using the transverse component seismograms. Because the sensor orientations of the borehole geophones were unknown, they had to be determined first. This was done using a novel method based on cross correlations between the geophones and their colocated surface accelerometer. In addition, by extensive cross-correlation analysis over the network, several installation inconsistencies were identified and resolved.