Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Hazard and Risk Assessment for
Induced Seismicity Groningen
Study 1 Hazard Assessment

Update 1 s t May 2015
Additional scenarios integrated

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Contents
Introduction ............................................................................................................................................................ 3
History of induced earthquakes in Groningen ................................................................................................... 3
Study and Data Acquisition Plan ............................................................................................................................. 5
Winningsplan 2013 ................................................................................................................................................. 6
Hazard and Risk Assessment .................................................................................................................................. 8
Scope and Expertise Required ............................................................................................................................ 8
Progress Probabilistic Hazard Assessment ......................................................................................................... 9
Schedule ........................................................................................................................................................... 10
Main new Elements Hazard Assessment – May 2015 .......................................................................................... 12
Rock Deformation – Compaction ..................................................................................................................... 12
Improvements for Version 1 (Mid 2015) ..................................................................................................... 12
Improvements for Version 2 (End 2015) ...................................................................................................... 12
Seismological Model ........................................................................................................................................ 12
Improvements for Version 1 (Mid 2015) ..................................................................................................... 12
Improvements for Version 2 (End 2015) ...................................................................................................... 12
Ground Motion................................................................................................................................................. 12
Improvements for Version 1 (Mid 2015) ..................................................................................................... 12
Improvements for Version 2 (End 2015) ...................................................................................................... 12
Gas production ................................................................................................................................................. 14
Rock Deformation - Compaction Modelling ..................................................................................................... 18
Results .............................................................................................................................................................. 19
Seismological Model ........................................................................................................................................ 21
Ground Motion Prediction ............................................................................................................................... 23
Peak Ground Acceleration ........................................................................................................................... 23
Spatial Variability ......................................................................................................................................... 24
Uncertainty .................................................................................................................................................. 24
Hazard Assessment ............................................................................................................................................... 25
Principles ...................................................................................................................................................... 25
Updates Hazard Assessment........................................................................................................................ 25
Sensitivity of the Hazard Assessment to Production........................................................................................ 28
Conclusion ............................................................................................................................................................ 31
References ............................................................................................................................................................ 32
Appendix A - Partners ........................................................................................................................................... 35
Appendix B - Experts ............................................................................................................................................. 36
Appendix C – Hazard Maps for the period 1/1/2015 to 1/1/2017 ....................................................................... 39
Appendix D – Large format Hazard Maps for better reading ............................................................................... 40

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Introduction
The people living in Groningen have been confronted with increasing intensity of the effects of induced
earthquakes. This has been the source of anxiety and frustration among the community. NAM, the ministry of
Economic Affairs, and regulator SodM face the challenge of formulating an adequate response to the induced
earthquakes. To that end, the currently existing instruments for assessing and mitigating these effects – as set
down in mining regulations, risk policies and, for example, building codes – need to be extended and made fitfor-purpose.
Therefore, a new risk methodology was developed and initially used in the Winningsplan 2013. This new
methodology combines NAM’s own internal safety standards, including the important role of monitoring,
national and international analogues. It will be progressed towards a dedicated risk assessment framework for
the Winningsplan 2016. For this latter purpose the risk methodology has been shared with the Groningen
Scientific Advisory Committee established by the Ministry of Economic Affairs (Ref. 17). This committee is
tasked to develop a national policy on risks associated with induced earthquakes. This policy will be used, per
decision on the Winningsplan 2013 (Ref. 19), to assess the Winningsplan 2016. Supporting elements, such as a
national annex to the Eurocode 8 Building Code addressing the fragility of buildings.
This Study 1 on “Hazard Assessment” addresses the ‘technical’ hazard elements of the risk methodology,
following the causal chain pictured in the subsequent paragraphs. This work has been well advanced since
December 2013, with key deliverables such as a seismological model and compaction based on subsidence
inversion now available. In Study 2 “Risk Assessment”, the risk methodology is described, following the same
causal chain as used in the current hazard study. This work covers for the first time a fully probabilistic risk
assessment, which as yet can only be used qualitatively as it awaits quantitative calibration following studies
such as site response measurements at the geophone network locations and a shake table test for a terraced
house. The two studies can be read independently. The additive attributes for the full risk dimension, including
the regional social impacts are to be merged into the composite ‘equation’ to evaluate the impact of gas
production1.
Data presented in this report should be read or interpreted with due caution taking into account the remaining
scientific uncertainties and further calibration, refining of models, validation taking place in 2015 and 2016.

History of induced earthquakes in Groningen
Since 1986, relatively small earthquakes have occurred near producing gas fields in the provinces of
Groningen, Drenthe and Noord-Holland. Over time, these events were considered to be a negative, but not an
insuperable, consequence of gas production. Since the Huizinge earthquake, however, it is recognized that the
earthquakes also pose a potential safety risk.
In the early 90’s, a multidisciplinary study was initiated by the Ministry of Economic Affairs and guided by the
above-mentioned Scientific Advisory Committee. This study focused on the relationship between gas
production and earth tremors. It was concluded that the observed earth tremors were of non-tectonic origin
and most likely induced by reservoir depletion (i.e., gas production). An agreement was set up with Royal
Dutch Meteorological Institute (KNMI) to install a borehole seismometer network in the Groningen area. The
network has been active since 1995 and was designed to detect earth tremors, pinpoint their locations and
quantify their magnitudes. Additional accelerometers were installed in areas with highest earth tremor
frequency.

1

This report is the report as indicated in article 6-1 of the decision from the Minister of Economic Affairs of 30
January 2015

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

1986
Early ’90
1995
1995
1995
1997
1998
2001
2003
2004
2004
2006
2009
2011
2012
Figure 1

First induced earthquake observed (Assen M= 2.8)
Multidisciplinary Study (1993) concluded:
“Earthquakes in North-Netherlands are induced by gas production”
Seismic network operational
KNMI estimates a maximum magnitude for Groningen: Mmax= 3.3
Agreement between NAM, Groningen and Drenthe on damage claim handling
Roswinkel earthquake with M= 3.4
KNMI adjusts estimate of maximum magnitude: Mmax= 3.8-4.0
Legal regulations damage claim handling set established by Parliament
Establishment of Tcbb (Technische commissie bodembeweging):
Technisch Platform Aardbevingen (TPA) established
KNMI adjusts estimate of maximum magnitude: Mmax= 3.9
First Probabilistic Seismic Hazard Analysis by TNO and KNMI
Westeremden earthquake with M= 3.4
Calibration study by TNO (Damage analysis)
Deltares assesses the Building Damage in Loppersum and confirms
Mmax= 3.9
Huizinge earthquake with M= 3.6

Sequence of main events until the earthquake of 16th August in Huizinge

Two factors triggered a renewed focus and widespread attention for the issue of seismicity induced by gas
production in Groningen. First, the earthquake near Huizinge (16 August 2012) with magnitude Mw=3.6 was
experienced as more intense and with a longer duration than previous earthquakes in the same area.
Significantly more building damage was reported as a result of this earthquake compared to previous
earthquakes. Second, a general realization and concern developed in society that seismicity in the Groningen
area has increased over the last years.
NAM reacted to these developments by initiating a series of new initiatives to better understand the
relationship between gas production and safety. These are described in the NAM “Study and Data Acquisition
Plan”, issued in October 2012 in support of a new Winningsplan 2013. This is further described in the next
section.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Study and Data Acquisition Plan
The Study and Data Acquisition Plan describes the relationship and goals of all study and research effort by
NAM and was shared with SodM and the Ministry of Economic Affairs (Ref. 1) in November 2012 and made
public early 2013. Regular updates of the study progress were reported to the advisory committee of the
Minister of Economic Affairs (TBO), the regulator (SodM) and her advisors (TNO-AGE and KNMI) and the
“Dialoogtafel Groningen”. The most recent update was reported to SodM in March 2015 (Ref. 13).
The main objectives of the plan are to:
1.
2.
3.

Understand the impact of the earthquake hazard on buildings and the safety of the community
Perform a fully integrated Hazard and Risk Assessment for the Groningen region, with all uncertainties
fully and consistently recognised and quantified
Identify and develop mitigation options:
Production measures
Pressure maintenance options
Optimised Structural Upgrading program:
o Identify highest risk buildings
o Establish optimal structural upgrading methodology

Other objectives are to:
4.
5.
6.

Address areas of different scientific views, and initiate additional studies or measurements to create
consensus,
Effectively monitor subsidence and seismicity,
Continuously improve our understanding of the physical mechanism leading to induced seismicity and the
resulting hazard and reduce the uncertainty in the hazard and risk assessment.

To achieve these objectives, NAM has sought the assistance and advice from external experts for each
expertise area from academia and knowledge institutes. The total cost of the study and data acquisition
program for the period 2014 – 2016 is estimated to be almost € 100 mln. This program is reviewed every 6
months and adjusted if necessary.
Some of the activities in the Study and Data Acquisition Plan are not expected to directly support the Hazard
and Risk Assessment of Winningsplan 2016. They rather serve to increase the understanding of physical
processes and therefore lend support and physical background to the hazard and risk assessments. These
activities are not expected to reach a level of maturity in the short term where they can be used to lend
support to predictions. Examples are, the planned laboratory experiments on the Zeerijp core to investigate
rupture and compaction processes in reservoir rock.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Winningsplan 2013
Intermediate results of the studies into induced seismicity carried out in 2013 were shared with the technical
advisory committee of the Ministry of Economic Affairs (TBO) at three two-day workshops held in May, July
and August 2013, and in several intermediate technical meetings focusing on specific technical issues. The
study results were reported to the Minister of Economic Affairs and SodM in November 2013 in the “Technical
Addendum to the Winningsplan - Groningen 2013” (Ref. 3, 4 and 5). This report also contained a probabilistic
Hazard Assessment complemented by a deterministic Risk Assessment.

•
•

Probabilistic analysis is based on chance incorporated in all uncertainties
Deterministic analysis is based on specifically defined scenarios

In addition to the Winningsplan 2013, NAM also issued a Borgingsprotocol and a Monitoringplan in December
2013, enabling regular revisits of the risk assessment on the basis of acquired monitoring data.
The aforementioned “Technical Addendum to the Winningsplan - Groningen 2013” (Ref. 4 and 5) gives a full
overview of the results of the studies carried out by NAM by the end of 2013.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Winningsplan 2016
The work done during 2013 provided new insights and received generally positive comments from peer
reviewers and the TBO, but was by no means conclusive or complete. Many technical questions remained
unresolved (Ref. 8 and 9), while uncertainties in the geomechanical parameters and in the estimated seismic
hazard were still large. Some of the remaining uncertainty stems from lack of knowledge and data (epistemic
uncertainty) and is therefore prone to be further constrained with ongoing data acquisition and analysis. The
“Study and Data Acquisition Plan” was therefore continued in 2014 and 2015 and will be continued in the
years thereafter.
The “Study and Data Acquisition Plan” is considered to be ambitious and comprehensive:
It involves many external entities: commercial parties, academics, university laboratories and
independent experts (Appendix A)
The scientific work is subjected to an extensive voluntary and compulsory assurance program, through
independent peer-review (Appendix B)
Bases hazard and risk assessments on evidence and data, not solely on expert opinion or expert
community consensus
The Scientific Advisory Committee (SAC) appointed by the Minister of Economic Affairs provides
independent oversight of the studies for the Winningsplan 2016
With the limited data available in 2013 to support or reject the available theories and models, the hazard
assessment in 2013 was intended to be conservative. With the ongoing acquisition of new data and the
progress of the studies, the hazard assessment will gradually become more reliable. Consequently, the
assessed hazard and its associated uncertainty are expected to decrease.
In January 2014, the Minister announced the intention to approve the Winningsplan Groningen 2013 subject
to the condition that NAM would submit a new Winningsplan in 2016 based on further and emerging insights
and study outcomes (Ref. 12). It was realized that the hazard could potentially increase (and there were more
uncertainties for the longer period of time) and that new insights were to be gained from ongoing studies and
monitoring. The final decision on the Winningsplan was made on 30 January 2015 (Ref. 19) with a number of
conditions. For the purpose of this report, the conditions in article 6 and in article 4 of the final decision from
February 2015, are most pertinent. Article 4 demands an assessment of the hazard and risks per relevant
region within the Groningen Field by 1st of May 2015. Several other conditions, e.g. the risk methodology,
production caps, monitoring requirements and mitigation measures in terms of structural upgrading, are
related to this hazard and risk assessment (as input or output) but are not discussed here.
The current report presents the intermediate update for mid-2015 (1 May 2015) of the Hazard and Risk
Assessment for Winningsplan 2016. Since these intermediate results are extracted from an on-going work plan
designed for delivery in 2016, they should be interpreted with caution given that some elements of the
models, which are currently significantly more advanced than those presented in the Winningsplan 2013, are
still evolving and maturing further using newly available data and recognizing that other improvements to
reduce the uncertainty and further data from the monitoring programme will only be incorporated in a next
version as they are currently not yet complete/mature.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Hazard and Risk Assessment
An important topic in NAM’s research program focuses on the assessment of the hazard and risk to which
people and buildings in the immediate vicinity of the gas field are exposed. The research on hazard and risk has
been split in two studies, as explained in the Introduction section. Study 1 discusses the hazard assessment.
The hazard is defined as: the annual frequency or probability, associated with different levels of ground motion,
at which buildings and other objects are exposed to earthquakes induced by the production of gas. A commonly
used measure of the hazard is the Peak Ground Acceleration (PGA).

Figure 3

Acceleration record for a typical strong tectonic earthquake, with the PGA indicated.

Other important parameters for characterizing the hazard include:
•

the spectral acceleration;

•

the duration of earthquake accelerations;

•

and the number of cycles.

A possible consequence of the seismic hazard is damage to, and in exceptional cases even collapse of,
buildings and other objects. To date no buildings have collapsed due to an earthquake. Potential injuries or
casualties for people located close to or inside these buildings can result from the shaking loose and falling of
building elements or from the (partial) collapse of buildings.
The hazard and the risk of building collapse and the subsequent impact on people is assessed by a statistical
methodology. The most widely used method is the Probabilistic Hazard and Risk Assessment or PHRA. The
statistical Monte-Carlo method is used to perform the calculations for this hazard and risk assessment. This
method entails repeated random sampling of the input variables to obtain numerical results for hazard and
risk. This method is a common approach in solving physical and mathematical problems. It allows the
uncertainties in all parameters to be consistently reflected in the PHRA, giving the full distribution of the
hazard and risk and therefore also the hazard and risk at a given exceedance level.

Scope and Expertise Required
The hazard and risk assessment needs to span from the cause (gas production) to the effect (injuries and
casualties). The uncertainties in each individual step need to be estimated and consistently incorporated in the
total assessment.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Figure 4

The Hazard and Risk Assessment requires a “bridge” to be built from the cause (gas production) to the effect
(building collapse and potential casualties).

The causal chain starts with gas production, reducing the gas pressure in the reservoir and causing
deformation of the reservoir rock. Deformation in turn can cause sudden movement in the subsurface, in
other words: seismicity. This compartment of the “bridge” is addressing processes in the deep subsurface;
the “geo-domain”. This requires geological, geophysical and geomechanical expertise. The seismicity
generated in the subsurface causes the ground motions or accelerations at surface which are affecting
buildings and people. The prediction of ground motion is therefore the crucial link between the processes in
the deep subsurface near the gas reservoir and the effects on buildings at the surface.
With sufficient knowledge of buildings, their structural strength, and of the presence of people in these
buildings (the exposure), the risks can eventually be assessed. This is described in Study 2. Especially expertise
in the civil engineering domain is vital to be able to carry out this assessment.

Progress Probabilistic Hazard Assessment
Based on the available earthquake catalogue and other data specific for the Groningen field, a probabilistic
seismological and hazard model was built in 2013. Where observational data was sparse or did not exist,
analogue data and methods from tectonic earthquake regions were used as the best available data in the
absence of appropriate data. This model formed the basis of the probabilistic hazard assessment supporting
the Winningsplan 2013. In this Winningsplan, hazard maps were presented that showed the PGA for a given
period, and with a given probability of exceedance level.
Relatively sparse observational data from the Groningen area was available at that time. Both the number of
earthquakes that had occurred and the number of observation sites were limited. From the start of
monitoring in 1994 till August 2012, some 188 earthquakes with magnitude larger than M=1.52 had been
recorded. For the prediction of the occurrence of larger events, NAM did not make an estimate of the hazard
based on theoretical considerations, which would need to be supplemented with potentially biased expert
judgment and the consensus views within the earthquake community. Instead, NAM prepared a hazard
assessment based on the scarce evidence available from the Groningen area, complemented, where
appropriate with evidence and methods derived from tectonic earthquakes (mainly in southern Europe). This
is a conservative approach: for low exceedance levels, the hazard is more likely to be adjusted downwards
than upwards, when updates are based on an expanding set of newly acquired acceleration data.
Hence, the acquisition of more data, the completion of more studies and the better quantification of
uncertainties, are very important. This led NAM in 2012 to embark on a large program to acquire more and
more relevant data. The main objective of this campaign is to make the hazard assessment more reliable. As
assumptions used tended to be conservative, the assessed hazard and its associated uncertainty are likely to
decrease. The various activities included in the data acquisition campaign are described below.

2

NAM is confident an earthquake with magnitude greater than or equal to M≥ 1.5 will be detected wherever
the earthquake occurred in the field and irrespective of its timing. An earthquake of smaller magnitude might
remain undetected, for instance, among the noise from activities at surface.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
In 2013, geophone strings were placed in the two existing deep monitoring wells (Zeerijp-1 and Stedum-1)
located in the Loppersum area, where seismicity is highest. With these two geophone strings placed at
reservoir depth (some 3000 m), even small earthquakes could locally be monitored and their origin
determined better relative to the interpreted fault system at reservoir level. Conclusions from the analyses of
data retrieved from these geofoons are:
• The recorded micro-seismic events are in accordance with KNMI observations
•

98.3% of the analysed events originate from the gas reservoir

•

Location of the events are in line with the known structural characteristics of the field

Early 2014, 10 additional GPS stations were placed to monitor subsidence better. In 2013 also a campaign
started to extend the existing geophone and accelerometer network. In 2014 some 42 shallow (200 m deep)
geophone wells were drilled with 4 geophones placed at 50 m intervals in each of these wells. In 2015, drilling
continues. Phase I of this project consisting of almost 60 geophone stations is expected to be completed mid2015. However, drilling will be continued with Phase II adding another 11 stations. At each of these stations
also a surface accelerometer will be placed.
In 2014 the first dedicated deep well designed for seismic monitoring was drilled at the Zeerijp location to a
depth below the Rotliegend reservoir. A second well will be spudded in May 2015. In this second well an
extensive reservoir section will be cored. Three laboratories are awaiting arrival of sections of this core to
perform rock experiments on both compaction and rupture processes. Mid 2015, NAM plans to install
geophone strings in these dedicated wells. Additionally, a geophone string will be placed in the existing
observation well Ten Boer-4, near the Eemskanaal cluster.
Each earthquake will now (depending on the magnitude) be recorded from multiple observation points. Based
on studies of the geophone and accelerometer data collected and compaction data measured from
experiments in laboratories, the hazard model can now, and will continue to be, improved. For each successive
improvement of the hazard model, based on studies and monitoring, conservatism in the model will be
reduced as conservative assumptions are replaced by constraints derived from actual field observations. This
means we feel confident that the assessed hazard at low exceedance levels of 0.2%/year or less is more likely
to decrease than increase overall as a result of further data collection and studies.

Schedule
Early 2014, the progress of the various studies and the status of the hazard and risk assessment were
reviewed. This underlined and clarified the interrelations between the various research activities and provided
an opportunity to re-direct the research effort towards resolving the largest uncertainties and the most
relevant research questions.
For each study domain, progress was envisaged with the hazard and risk model increasingly being refined and
the model parameters improved.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Figure 5

Schedule for the research program for the Winningsplan 2016 as presented in the “Study and Data
Acquisition Plan“.

Successive improvements at the half-yearly status reviews will be used to re-direct and optimise the research
efforts. This is further discussed for each domain in the next sections. Note that the initial timeframe for the
studies and half-yearly updates was different from the current timeframe as introduced by the February 2015
decision on the Winningsplan 2013 (Ref. 12).
Table 1 shows the current schedule for updates of the hazard and risk assessment in preparation of the
Winningsplan 2016.
Target Date
1st January 2015

Maturity
Version
0

1st May 2015

1

1st January 2016

2

st

1 July 2016
Table 1

3

Status of Hazard and Risk Assessment
Demonstrate capability to extend the probabilistic hazard assessment into the risk
domain.
First probabilistic Hazard and Risk Assessment. Important elements of the hazard
assessment still in development (in particular site response).
First version with probabilistic Risk Assessment for identification of most fragile buildings
to optimise the structural upgrading program.
Include site response into the ground motion prediction methodology. Hazard and Risk
Assessment with most important input included.
Final Hazard and Risk Assessment for Winningsplan 2016. The results of the full research
effort is included in this assessment.

Main deliverables for each inventory update of the hazard and risk assessment

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Main new Elements Hazard Assessment – May 2015
This section presents the progress made in the probabilistic hazard assessment since the Winningsplan 2013
was submitted on 29th November 2013. The hazard assessment for Winningsplan 2013 was the first
probabilistic hazard assessment for induced seismicity in Groningen. The current probabilistic hazard
assessment builds on the work presented in the Winningsplan 2013 (Ref. 3) and the accompanying Technical
Addendum (Ref. 4 and 5).
The further study work into induced seismicity in Groningen towards Winningsplan 2016 has been described in
the “Study and Data Acquisition Plan” and the accompanying Study Catalogue. Below summarises the main
improvements incorporated in the Hazard model for this assessment (mid 2015) and the expected
improvements for the next assessment (late 2015) per category.

Rock Deformation – Compaction
Improvements for Version 1 (Mid 2015)
Inversion from subsidence by using optical leveling survey data up to 2008.
Improvements for Version 2 (End 2015)
Enhance inversion from subsidence by using additional optical leveling survey data 2013 and InSar data.
Improved porosity model for the reservoir from detailed facies modelling and seismic inversion
techniques for compressibility estimation.

Seismological Model
Improvements for Version 1 (Mid 2015)
Activity Rate model for seismicity
Integration between inversion from subsidence and activity rate model
Confirmation from deep geophone wells that the hypo-centers of the earthquakes are in the reservoir
with a small number of earthquakes possibly in the Zechstein.
Improvements for Version 2 (End 2015)
Investigate evidence for potential changes in b-value – with time, space, strain, strain rate
Investigate evidence for spatial-temporal bias in activity rates – scope for refining extended activity rate
model
Investigate evidence for rate or delay effects following production changes
Establish Bayesian framework for ranking performance of alternative models
Utilize data from the upgraded monitoring network
Investigate influence of finite ruptures along mapped faults

Ground Motion
Improvements for Version 1 (Mid 2015)
Groningen-specific equations for spectral accelerations as well as PGA
Expanded dataset of Groningen ground-motion records
Epistemic uncertainty in Ground Motion Prediction Equations (GMPEs), due to extrapolation to larger
magnitudes, in logic-tree branches
Sigma models for GMPEs calibrated to local data, with adjustments for point-source distance metric at
larger M
Preliminary model for prediction of durations, calibrated to Groningen recordings
Model for correlation of predicted values of spectral acceleration and duration
Improvements for Version 2 (End 2015)
More accurate modelling of near-source attenuation of accelerations due to high-velocity layers above
reservoir

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Improved model for durations, capturing very short durations in epicentral area and swift prolongation
with distance, including enhanced model for the correlation of accelerations and duration
Site-specific soil amplification terms giving more realistic spectral shapes and reduced sigma’s in GMPEs
Non-linear site response capturing reduced soil amplification with increased acceleration in base rock
horizon
Investigate strength limitations on maximum surface accelerations transmitted by very soft/weak soil
layers
Investigate influence of finite ruptures along mapped faults
The activities planned to further improve the hazard assessment are all discussed in the “Study and Data
Acquisition Plan” issued early 2015 and the accompanying studies catalogue (Ref. 13). Progress will be
reviewed twice a year and the research program re-directed if required. In case of a significant adjustment, an
update of the “Study and Data Acquisition Plan” will be issued.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Gas production

Figure 6
The first section of the causal bridge starts with the cause, gas production, and the effect of
the resulting pressure drop in the reservoir on the reservoir rock.

In both studies (hazard and risk assessments) two production scenarios are used to evaluate the hazard and
risk. These scenarios are:
Scenario I

The total gas production from the Groningen field in this scenario is limited to 39.4 Bcm/year.
Additionally, 4 regional production caps are imposed. These regional caps are imposed on the
clusters in regions defined as East (24.5 Bcm/year), LOPPZ (3 Bcm/year3), South-West (9.9
Bcm/year) and Eemskanaal (2.0 Bcm/year). Together the regional caps sum up to the field
production limit of 39.4 Bcm/year. A consequence is a relatively imbalanced load-factor
distribution over the field, highest on Eastern clusters and lowest on LOPPZ clusters.
Operational flexibility is further limited by the Eemskanaal gas quality issue (Ref. 18), gasdistribution over the ring pipeline system connecting the production clusters with the
custody transfer stations (overslagen) and filling up of the Underground Gas Storage in Norg
during the summer months.
This scenario is based on the Ministerial decision of February 2015 (Ref. 19; article 5).

3

The ruling of the Council of State to further reduce LOPPZ to nil is not incorporated in this scenario given the
limited time for modelling since the date of this ruling (14th April 2015) and because this ruling does not rule
out that 3 Bcm may be produced if necessary for security-of-supply reasons. This scenario is therefore a
conservative approach for the Loppersum area.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Figure 7

Scenario II

An indicative gas production schedule for scenario I. Production is kept below 39.4 Bcm,
until the natural decline of the production from the field sets in. No additional
development wells are drilled.

In this scenario the field production is limited to 33.0 Bcm/year, while the imposed regional
caps remain unchanged and defined as East (24.5 Bcm /year), LOPPZ (3 Bcm /year), SouthWest (9.9 Bcm/year) and Eemskanaal (2 Bcm /year). The 33 Bcm annual gas production
volume is the minimum volume to cover GasTerra’s portfolio, with a pre-set monthly volume
distribution. Operational flexibility is dictated by the Eemskanaal quality issue, filling up
during the summer season of the Underground Gas Storage in Norg and gas-distribution in
cooperation with GasUnie gas-quality management.

Figure 8

An indicative gas production schedule for scenario II. Production is kept below 33.0 Bcm,
until the natural decline of the production from the field sets in. No additional
development wells are drilled.

This scenario is based on the letter from the minister announcing his decision to reduce the
production in the first half of 2015 to 16.5 Bcm. In this scenario, it is assumed that in the
second half of 2015 the production will be limited to the same volume as in the first half.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Scenario III

In this scenario the field production is limited to 33.0 Bcm/year from 2016 onwards and
further reduced to 21.0 Bcm from 1-1-2020. This is thought to be the earliest data the
additional gas blending capacity to displace production from the Groningen field in the
market will be available, until the natural decline of the production from the field sets in. No
additional development wells are drilled.
40

Scenario 21 BCM

35

Annual Production (BCM TQ)

30

25
EKL
LOPPZ

20

S-W
East

15

10

5

0
2015

Figure 9

2016

2017

2018

2019

2020

2021

2022

2023

2024

2025

2026

2027

2028

2029

2030

An indicative gas production schedule for Scenario III. Production is kept below 33 Bcm
from 2016 onwards and further reduced to 21.0 Bcm from 1-1-2020 (as soon as
additional gas blending capacity is available), until the natural decline of the production
from the field sets in. No additional development wells are drilled.

To demonstrate the impact of the progress in the hazard assessment methodology, an additional hazard
assessment was carried out using the base production scenario of the update of the Winningsplan 2013.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Figure 10

Spatial and temporal production caps have been imposed. Production caps have been imposed on 5 groups
of production clusters. Additionally, the production has been capped for the first and second half of 2015.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Rock Deformation - Compaction Modelling
For the seismic hazard maps in the Winningsplan update 2013, three compaction models were used: bi-linear,
time decay and isotach (Ref. 4). These models assume a relationship between compaction and porosity. These
models produced local second order biased estimates of subsidence as evidenced by the spatio-temporal
patterns in the residuals when compared to the levelling data. A direct inversion of the levelling data to
compaction was identified as a useful alternative method to estimate the compaction grid of the Groningen
field. It was demonstrated (Ref. 23) that it is indeed feasible to derive spatially smooth compaction estimates
from the levelling on a course grid (2.5 X 2.5 km) using a homogeneous half space model with a Poisson’s ratio
of 0.25. Each block in the grid returns in this case a different compaction value (Fig. 11). The study showed that
a basic (‘first-order’) forward simulation model with constant rates of compaction per unit of pore pressure
decline per reservoir grid block performed well in its ability to explain the variation in subsidence
measurements. This linear relationship was used for a base case compaction scenario to forecast the seismic
hazard in the near future (2016-2021).
In addition, both the time decay and RTCiM compaction models (Ref. 4) were used as separate sensitivity
scenarios to reflect the compaction model uncertainty in the hazard calculations. The RTCiM replaces the
isotach model, mainly because TNO used the RTCiM as the base case compaction model in their latest reports
(Ref. 7), thus allowing for better comparison.
The main difference with the compaction scenarios in the Winningsplan update 2013 is the decoupling of
compressibility and porosity. Another main difference is that the compaction as calculated for the grid blocks
in 2013, should be similar for all compaction models. All compaction models use a homogenous half-space
model to estimate subsidence from compaction and vice versa rather than the rigid-basement model that was
used in the Winningsplan 2013 update. This means that individual input parameters of the compaction models
but also compaction values will not be one-to-one comparable.

Figure 11

Example of a compaction grid calculated from the levelling surveys for the period 1972-2008.

18

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Results
As a base case the linear compaction–pressure drop relation inferred by inversion from the subsidence
measurements for the different blocks was used to predict the compaction for the period 1-7-2016 to 1-72021, using forecasted reservoir pressure grids for the two production scenarios. Also the effect of different
compaction models was investigated (time-decay and RTCiM). Figure 12 shows the cumulative compaction
from the start of production to 2021 for the two production scenarios using the linear compaction model. The
impact of the two production scenarios on cumulative compaction is limited because of the short additional
time period (5 years) compared to the time the field has been producing already. This is especially the case in
the area of highest compaction.
Period: 1963-2021

Figure 12

Cumulative compaction from the start of production to 2021 for both production scenarios based on the
inversion of levelling data (linear compaction model)

Figure 13 shows the compaction for the period 1-7-2016 to 1-7-2021 for both production scenarios. AS the
results show, the difference between both is small. These findings are in line with earlier published work on
the impact of the Eemskanaal cluster on compaction assessment (Ref 18).
Period: 1-7-2016 / 1-7- 2021

Figure 12

Compaction for the period 1-7-2016 to 1-7-2021 for both production scenarios using the linear compaction
model

The impact on additional compaction in the period between 1-7-2016 and 1-7-2021, using alternative
compaction models, is presented in Figure 14 for the 39.4 Bcm/year scenario. This show that there is still
uncertainty remaining in the compaction assessment. This is an important contributor to the uncertainty in the
hazard and risk assessment.

19

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Period: 1-7-2016 / 1-7- 2021

Figure 14

Compaction for the period 1-7-2016 to 1-7-2021 for the three compaction models (39.4 Bcm production
scenario)

20

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Seismological Model

Figure 15

The causal bridge continues with seismicity resulting from the deformation of reservoir rock and the
prediction of the ground motion (PGA).

The logical first step in the Probabilistic Hazard and Risk Assessment (PHRA) workflow is the Seismological
Model - this is a model which allows synthetic earthquake catalogues, detailing event locations, occurrence
times and magnitudes, to be calculated given their joint probability distributions based on a model of the
underlying geomechanical process. In PHRA for naturally occurring tectonic earthquakes, the seismological
model usually comprises an identified seismically active region with assumed parameter values specifying the
expected level of seismic activity. In the Groningen case, reservoir compaction has been identified as the
geomechanical process inducing the seismicity. The seismological models have been built on this basis. For the
2013 Winningsplan submission, the seismological model used in the PSHA calculations was based on earlier
work by Kostrov and McGarr which linked the total seismic moment of a catalogue of events to the subsurface
strains causing them. A strain partitioning factor was introduced to account for the observed division of strain
into seismogenic and aseismic components.
An alternative to forecasting total seismic moment according to strain is to forecast the occurrence rate of
events above a certain magnitude according to strain. Models of both types are seen in the literature and the
choice between them is ultimately an empirical question: which type of model best fits the observed data? In
the Groningen case, we see a more precise relationship between event rate and reservoir strain than we do for
total seismic moment. Moreover, event rate based models can be naturally extended to incorporate aftershocks. This is particularly useful as it has already been shown that spatial and temporal clustering of events
needs to be accounted for in the Groningen earthquake catalogue. For these primary reasons, an Activity Rate
model incorporating an Epidemic Type Aftershock Sequence (ETAS) model has been developed as a second
generation seismological model. The performance of this model was further improved by also accounting for
the influence of pre-existing fault offsets. A simple geometric argument can be used to show that the induced
strain on a pre-existing vertical fault in a compacting reservoir is proportional to the product of fault offset and
reservoir compaction. Generalising this simplified geometry it can be shown that replacing compaction in the
initial version of the Activity Rate model with a strain-thickness attribute accounts for reservoir compaction
and reservoir dip including fault offsets.

21

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
As well as accounting for the variation of seismicity with the process of reservoir level compaction, the
seismological model must also account for the observed statistics of earthquakes magnitudes, in particular the
relative abundance of large and small magnitude events described by the Gutenberg-Richter b-value.
Consideration of the Groningen catalogue as a whole gives a b-value very close to the value of 1.0, generally
found for earthquake populations elsewhere. If, however, the catalogue is subdivided into smaller subsets
according to the strain-thickness attribute, then potentially significant systematic variations of the b-value with
strain-thickness become apparent with b tending to smaller values at larger values of strain thickness.
Although a systematic variation of the b-value is seen, the error bounds on the values obtained are large due
to the reduced number of events considered in each subset. For this reason a constant b-value close to 1.0
calculated for the catalogue as a whole is taken as the base case scenario with an alternative upper bound
scenario determined by taking the b-value as a stochastic function of the strain-thickness. The lower bound
scenario was taken as having the constant b-value used for the base-case but maximum likelihood values of
the Activity Rate and ETAS model parameters rather than samples drawn from the joint multi-parameter
distribution.

22

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Ground Motion Prediction
Peak Ground Acceleration
At the time of the preparation of Winningsplan 2013, relatively few earthquake acceleration records were
available and therefore little data on which to base a ground motion prediction methodology. This was caused
by the relatively low number of earthquakes causing measurable ground accelerations and the relatively low
number of accelerometers placed over the field, recording these earthquake accelerations. Although the
number of earthquakes with significant accelerations measured at surface increased from 8 to 12 from
Winningsplan 2013 to this assessment, the number of recordings of these earthquakes increased from 40 to
85. This is mainly due to the increased number of recording sites as the first geophone sites with
accelerometers of the network extension have now been taken into operation. Since the assessment was
started two more earthquakes have occurred, each triggering 14 accelerometers and raising the number of
recordings to 113.
The acceleration records currently available in the Groningen area are for low magnitude earthquakes (M≤3.6),
which are capable of causing damage to buildings, but are considered to be too small to cause buildings to
collapse. For the hazard and risk assessment the ground motion for larger magnitude earthquakes are
important. To achieve this, the available data needs to be extrapolated to larger magnitude earthquakes.
Within the available time for Winningsplan 2013, a model derived from recordings of tectonic earthquakes in
southern Europe was used. Because equations were used that were intended for much stronger tectonic
earthquakes, the hazard associated with larger magnitude earthquakes was in hindsight overstated in the first
pass in the Winningsplan 2013 (Ref. 4; Chapter 7). The latest studies (Ref. 24) now show that for an earthquake
of a given magnitude the ground accelerations are smaller at short periods (e.g. PGA).

Figure 16

Variation in the median GMPE with epi-central distance (left) and the associated variability (right) for a (top
row) M4.0 and (bottom row) M5.0

Due to the larger number of installed accelerometers in the field, more data is currently available for the
preparation of a Groningen specific ground acceleration methodology. Using the additional acceleration
records, first an assessment was made of the range of accelerations at surface that larger earthquakes could
impose. This is based on a simulation approach. This resulted for the best estimate in a lower assessment of
the hazard for earthquakes with a larger magnitude (Ref. 24).

23

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
In this update of the hazard assessment not only PGA is evaluated, but additionally spectral accelerations and
the duration of the acceleration are evaluated. This is important for the risk assessment, as building response
to the hazard critically depends on these parameters (see next section).
Spatial Variability
Apart from the average acceleration also the spatial variability of the acceleration resulting from a single
earthquake is important. There are many reasons for the large variability in the accelerations measured by
different stations, due to a single earthquake. Within the determining factors, the local soil conditions are very
important. Accelerations at very soft sites, like peat areas, are in general higher than at less soft sites like sand
areas. NAM has therefore asked Deltares to carry out a detailed study of the shallow geology of Groningen
(Ref. 25 and 26). Together with experiments planned mid-2015 at the geophone locations and modelling of the
site response, a basis will be created for the next update of the ground motion prediction methodology for the
Groningen area, due by the end of 2015.
In the Winningsplan 2013, a database of tectonic earthquake recordings mainly in southern Europe and Turkey
was used. Of course, the variability in the shallow geology over such a large area is much larger than that over
the Groningen area. It is therefore likely that also the variability in the accelerations was overestimated for the
Winningsplan 2013. The studies of the shallow geology of Groningen and the planned experiments at the
geophone / accelerometer stations are expected to lead to a further reduction of the uncertainty in the
assessment for the majority of soil types. The outcome of these experiments at the geophone / accelerometer
stations, that are expected to commence late April 2015, are crucial to confirm this.

Figure 17

Results of a simulation of earthquake waves moving towards the surface.

Uncertainty
To reflect the remaining epistemic uncertainty in the final ground motion prediction, three methodologies are
weighted (a low, mid and high case). These are combined to form the mean case using weight factors of 20%,
50% and 30% respectively. The high case is still based on tectonic earthquakes and is similar to the method
used for the Winningsplan 2013, the mid and low case are based on simulation based extrapolation of the
Groningen accelerometer data to higher magnitudes.

24

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Hazard Assessment
Principles
Data presented in this report should be interpreted with due caution taking into account the remaining
scientific uncertainties and further calibration, refining of models, validation taking place in 2015 and 2016.
For the probabilistic description of the ground accelerations (PGA) a hazard map is used. On this map for each
location the acceleration is plotted that could, with a prescribed probability (exceedance level), be exceeded in
a prescribed period. Hazard levels are shown using a gradual colour scales, with contours of equal hazard, i.e.
PGA, added for convenience.
Hazard maps can be made for different production scenarios. An example are the two hazard maps prepared
late 2014 (Ref. 18) using the updated model of the reservoir (Figure 18), the activity rate seismicity model and
the RTCiM model to predict compaction. These maps were prepared for a probability of exceedance
(exceedance level) of 2%/year for the period 2017 to 2027.
The map on the left-hand side is based on the gas production as foreseen by NAM in the Winningsplan 2013,
while the map on the right includes the production caps imposed early 2014 by the Minister of Economic
Affairs. The yellow to red colour scale indicates the PGA as a fraction of g (the average free-fall acceleration in
the gravitational field of the earth). Contours at intervals of 0.02 g are added.
Period: 2017 / 1-7- 2027

Figure 18

Hazard map showing the peak ground acceleration (PGA) with 2 % average annual chance of exceedance
from 2017 to 2027 and the Activity Rate seismological model. The contour interval is 0.02 g.

Updates Hazard Assessment
The construction of the hazard maps shown in this section requires clarification. A location in the Groningen
field during a period of 5 years is subjected to accelerations resulting from induced earthquakes. At some
locations, e.g. near Loppersum, the chance of experiencing a large acceleration is higher than at the periphery
of the field. The chance of experiencing an acceleration in excess of a certain peak ground acceleration value
declines with larger accelerations. This is shown for a large set of locations in figure 19. Each declining line
corresponds to a single location in the field.

25

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Figure 19

Annual exceedance rate for peak ground acceleration at different locations in the field. This was assessed
for the period 2016 – 2021 and the 39.4 Bcm production scenario. Each line corresponds to a location in the
field. The bold line indicates the maximum PGA in the field for a given exceedance level (bounding
envelope).
How to read this figure: The red line indicates that for an exceedance level of 0.2%/year the highest PGA felt
in the field is 0.35g.

26

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
A weighted ground-motion prediction methodology was used to assess the hazard. A low, mid and high case
GPME model were combined to arrive at the (weighted) medium ground motion prediction to create the mean
hazard map. The resulting mean hazard map is shown below, in figure 20. This map is the basis for the risk
assessment in Study 2.
Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 39.4 bcm/year

Max PGA = 0.35 g
Figure 20

Mean hazard map for period 1-7-2016 – 1-7-2021, Production: 39.4 Bcm/year, Compaction: Inversion Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10% chance in 50 years).

27

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
The hazard map based on the high case GMPE model is presented in figure 21.
High - period: 1-7-2016 / 1-7- 2021 – Production: 39.4 bcm/year

Max PGA = 0.57 g
Figure 21

High Hazard map for period 1-7-2016 – 1-7-2021, Production: 39.4 Bcm/year, Compaction: Inversion-Linear,
Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10% chance in 50 years).

Sensitivity of the Hazard Assessment to Production
As a sensitivity, mean hazard maps for the medium ground motion prediction are shown below (Fig. 22), for
the 39.4 Bcm/year production scenario, the 33 Bcm/year production scenario, the 21 Bcm/year production
scenario and the production scenario used in the update of the Winningsplan 2013 (with the latest model
updates). As the production in the Loppersum area is reduced to a maximum of 3 Bcm/year for in all
production scenarios, the effect of the further reduction in production is minimal in the Loppersum area. This
can clearly be seen in the maximum PGA values for these maps (which occur in the Loppersum area).
There is a marked difference in maximum PGA between the production scenario for the update of the
winningsplan 2013 and the other three production scenarios. This clearly shows the progress made in the
hazard assessment methodology since the submission of the 2013 update of the winningsplan at 29th
November 2013 and the effectiveness of the measures taken.

28

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Figure 22

39.4 Bcm / year

33 Bcm / year

Max PGA = 0.35g

Max PGA = 0.34g

21 Bcm / year

Production Scenario
Update Winningsplan 2013

Max PGA = 0.34g

Max PGA = 0.43g

Mean hazard maps for period 1-7-2016 – 1-7-2021, four production scenarios are shown: 39.4 Bcm/year, 33
Bcm/year, 21 Bcm/year and the scenario used for the update of the winningsplan 2013. Compaction:
Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10% chance in 50
years).

29

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Production Scenario

Linear

Time Decay

RCTiM

Max PGA = 0.35g

Max PGA = 0.42g

Max PGA = 0.41g

Max PGA = 0.34g

Max PGA = 0.40g

Max PGA = 0.38g

Max PGA = 0.34g

Max PGA = 0.40g

Max PGA = 0.40g

Max PGA = 0.43g

Max PGA = 0.46g

Max PGA = 0.40g

39.4 Bcm / year

33 Bcm / year

21 Bcm / year

Update Winningsplan 2013

Figure 23

Mean hazard maps for period 1-7-2016 to 1-7-2021 for the three Compaction Models and four production scenarios are shown. Activity Rate: V1, M ≥ 3.5. GMPE is V1-mean.
Metric shown is 0.2% year-1 chance of exceedance (10% chance in 50 years).

30

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Conclusion
1.

The Huizinge earthquake on August 16, 2012 was a watershed event for gas production in the
Groningen field, causing NAM to launch a comprehensive Study and Data Acquisition Plan for induced
seismicity in Groningen. This Plan builds on earlier seismic research and is a crucial building block for the
Winningsplan, due July 1, 2016. The aim of the Plan is to deliver both a Hazard Assessment (i.e., ground
motions) and a Risk Assessment (i.e., harm to people) for induced seismicity in the Groningen area.

2.

The Hazard Assessment update presented in this study is an intermediate step in the execution of the
Study and Data Acquisition Plan:
a.

Our understanding of the seismic hazard has benefited from fresh data obtained from the
extended network of geophones and accelerometers, put in place in the second half of 2014. This
has helped to refine our modeling of the seismic hazard.

b.

Compared with the results obtained for the 2013 Winningsplan, the current update shows a
meaningful reduction of the assessed seismic hazard, translating into geographical maps with
lower PGA hazard.

c.

Comparison of the hazard for the three production scenarios (39.4 Bcm/year, 33 Bcm/year and
21 Bcm/year) shows the maximum hazard is for all three scenarios located in the Loppersum
Area. The limited impact of the annual field production on the maximum hazard is mainly the
result of the production cap for the Loppersum area, which has been implemented for each of
these three scenarios.

d.

For a comparison, the hazard has also been evaluated for the production scenario of the update
of the Winningsplan 2013. This shows that the hazard assessment has reduced since this
Winningsplan was issued in November 2013. This is the result of the restriction of the annual
production from the clusters in the Loppersum area and improvements in the hazard assessment
methodology.

3.

An important next step in the Study and Data Acquisition Plan is to further refine the Hazard
Assessment by modeling the non-linear soil response using the recently completed Deltares description
of the local shallow subsurface and new measurements of soil response.

31

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

References
The references in this list have been placed in chronological order of publication.
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2012,
http://www.rijksoverheid.nl/documenten-en-publicaties/rapporten/2013/01/25/planning-report-study-anddata-acquisition-plan-for-induced-seismicity-in-groningen.html
Staatstoezicht op de Mijnen, Reassessment of the probability of higher magnitude earthquakes in the
Groningen gas field, 16th January 2013
http://www.sodm.nl/sites/default/files/redactie/rapport%20analyse%20aardbevingsgegevens%20gronings
e%20gasveld%2016012013.pdf
Nederlandse Aardolie Maatschappij BV, Update of the Winningsplan Groningen 2013, 29th November
2013.
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Nederlandse Aardolie Maatschappij BV (Jan van Elk and Dirk Doornhof, eds), Technical Addendum to the
Winningsplan Groningen 2013; Subsidence, Induced Earthquakes and Seismic Hazard Analysis in the
Groningen Field,
http://www.rijksoverheid.nl/onderwerpen/aardbevingen-in-groningen/documenten-enpublicaties/rapporten/2014/01/17/bijlage-1-analyse-over-verzakkingen-geinduceerde-aardbevingen-enseismische-risico-s.html
Nederlandse Aardolie Maatschappij BV (Jan van Elk and Dirk Doornhof, eds), Supplementary Information
to the Technical Addendum of the Winningsplan 2013.
http://www.rijksoverheid.nl/documenten-en-publicaties/rapporten/2014/01/17/toelichting-op-gewijzigdwinningsplan-groningenveld.html
Arup Project Title: Groningen 2013, Implementation Study
http://www.rijksoverheid.nl/onderwerpen/aardbevingen-in-groningen/documenten-enpublicaties/rapporten/2014/01/17/arup-rapport.html and
http://www.rijksoverheid.nl/onderwerpen/aardbevingen-in-groningen/documenten-enpublicaties/rapporten/2014/01/17/oplegnotitie-van-de-nam-op-het-arup-rapport.html
TNO, A general framework for rate dependent compaction models for reservoir rock, 2013, Report TNO
2013 R11405
TNO, Eindrapport - Toetsing van de bodemdalingsprognoses en seismische hazard ten gevolge van
gaswinning van het Groningen veld, 2013, Report TNO 2013 R11953.
http://www.rijksoverheid.nl/onderwerpen/aardbevingen-in-groningen/documenten-enpublicaties/rapporten/2014/01/17/toetsing-tno-van-de-bodemdalingsprognose-en-seismische-hazard-tgvgaswinning-van-het-groningen-veld.html
Staatstoezicht op de Mijnen, Advies Staatstoezicht op de Mijnen: Winningsplan Groningen 2013.
http://www.sodm.nl/sites/default/files/redactie/advies%20sodm%20winningsplan%20groningen%202013.p
df
Staatstoezicht op de Mijnen – Advies Winningsplan 2013 / Meet- en Monitoringsplan NAM Groningen
gasveld.
http://www.rijksoverheid.nl/documenten-en-publicaties/rapporten/2014/01/17/adviezen-sodm.html
SodM, Risico Analyse Aardbevingen Groningen, 2013
Ministry of Economic Affairs, The cabinet decision on production from the Groningen field.
http://www.rijksoverheid.nl/onderwerpen/aardbevingen-in-groningen/documenten-enpublicaties/kamerstukken/2014/01/17/gaswinning-in-groningen.html
Nederlandse Aardolie Maatschappij BV, Jan van Elk & Dirk Doornhof, Study and Data Acquisition Plan
Induced Seismicity in Groningen for the update of the Winningsplan 2016, December 2014, submitted in
March 2015, EP 201503202325 .
Bourne, S. J., S. J. Oates, J. van Elk, and D. Doornhof (2014), A seismological model for earthquakes
induced by fluid extraction from a subsurface reservoir, J. Geophys. Res. Solid Earth, 119, 8991–9015,
doi:10.1002/2014JB011663.)
http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014JB011663/ or
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32

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
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S.J. Bourne, S.J. Oates, J.J. Bommer, B. Dost, J. van Elk, D. Doornhof, A Monte Carlo method for
probabilistic hazard assessment of induced seismicity due to conventional gas production, Bulletin of the
Seismological Society of America, V.105, no. 3, June 2015 in press.
Magnitude, Barnavol, J., Belayouni, N., Daniel, G. and Fortier, E., Seismic Monitoring, Delivery of location
Results – Groningen field, January 2015.
Nederlandse Aardolie Maatschappij BV, Risk Methodology; Back to the region, February 2015, (forwarded
to the national committee on earth quake related risks in April 2015) (EP 201504200668).
Nederlandse Aardolie Maatschappij BV, Hazard Assessment for the Eemskanaal area of the Groningen
field, November 2014.
Besluit van de Minister van Economische Zaken: Instemming gewijzigd Winningsplan Groningen veld,
Ministerie van Economische Zaken, February 2015, ETM/EM/13208000.
Stephen Bourne and Steve Oates, Activity Rate Model.
Letter from the Minister of Economic Affairs: Reductie van de productie van het Groningen veld eerste
helft 2015, 10th February 2015.
Matt Pickering, A re-estimate of the earthquake hypo-centre locations in the Groningen Gas Field, March
2015.
Regularised direct inversion to compaction in the Groningen reservoir using measurements from optical
levelling campaigns, S.M. Bierman, F. Kraaijeveld and S.J. Bourne, March 2015.
Development of Version 1 GMPEs for Response Spectral Accelerations and for Strong-Motion Durations,
Julian J Bommer, Peter J Stafford, Benjamin Edwards, Michail Ntinalexis, Bernard Dost and Dirk
Kraaijpoel, March 2015.
Introduction to the Geology of Groningen, Erik Meijles, April 2015.
Geological schematisation of the shallow subsurface of Groningen (For site response to earthquakes for
the Groningen gas field), Deltares Pauline Kruiver and Ger de Lange.
Exposure Model v1 – Updated Typologies and Inference Rules, Helen Crowley, Damian Grant and Rui
Pinho, March 2015.
Report on software verification against experimental benchmark data, Mosayk, November 2014
Report on structural modelling of non-URM buildings, Mosayk, April 2015
URM Modelling and Analysis Cross Validation – Arup, EUCENTRE, TU Delft, Reference
229746_032.0_REP127_Rev.0.03 April 2015.
Plan of approach for URM material testing, ARUP, Eucentre and TU Delft, March 2015.
Report on v0 Partial Collapse Fragility Functions, Helen Crowley and Damian Grant, October 2014
Development of v1 Fragility Functions for Structural Failure, Helen Crowley, Damian Grant and Rein de
Vries, April 2015
Analysis of deep compaction measurements in the Groningen field, Pepijn Kole, Dirk Doornhof and
Antony Mossop, May 2015 (in preparation)
SodM, “P500 Engels ref-06-risico-analyse-aardgasbevingen-groningen”
TNO, “TNO 2013 R12071, Safety considerations for earthquakes (2013); Steenbergen, R.D.J.M.;
Vrouwenvelder, A.C.W.M.; Scholten N.P.M. (ERB)”
SodM, Letter on reporting requirements as part of the final decision on the winningsplan, annex “SodM
expectations for NAM 1st of May risk report”, 31 March 2015, 15046197

33

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Note: For each document the link to the document on the web-site, where the document was issued has been
provided. Some of these links might have become obsolete.
For those documents without a current link, a link to a www.namplatform.nl site will be provided in the next
update of the report.

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Appendix A - Partners
The main partners in the research program into induces seismicity in Groningen are listed below:
Partner
Deltares
University Utrecht (UU)
University Groningen (RUG)
ARUP
Technical University Delft (TUD)
Eucentre, Pavia, Italy

Expertise
Shallow geology of Groningen, soil properties and measurements of
site response/liquefaction.
Measurements of rock compaction and rupture on core samples,
understanding of physical processes determining compaction.
Shallow geology of Groningen.
Modelling of building response to earthquakes, management of the
program to measure strength of building materials.
Measure strength of building materials and building elements.

Mosayk

Measure strength of building materials, building elements and shake
table testing of full scale houses.
Modelling of building response to earthquakes.

Magnitude

Seismic Monitoring (determination of location results deep geophones)

(A Baker Hughes & CGG Company)

TNO

Baker-Hughes

Potential for earthquakes resulting from injection.
Building sensor project.
Supplier of geophone equipment permanent seismic observations
wells.
Supplier of geophone equipment temporary observation wells.

Anthea

Management of the extension of the geophone network.

Rossingh Drilling

Drilling of the shallow wells for the extension of the geophone
network.

Avalon

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Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Appendix B - Experts
Apart from scientist, engineers and researchers in NAM and the laboratories of Shell (Rijswijk) and Exxonmobil
(Houston), NAM has also sought the advice of internationally recognised experts. Some of the experts
involved in the research program on induced seismicity in Groningen, led by NAM, are listed below.

External Expert

Affiliation

Role

Main Expertise Area

Gail Atkinson

Western University,
Ontario, Canada

Independent Reviewer

Ground Motion Prediction

Sinan Akkar

Bogazici, University
Istanbul

Collaborator

Ground Motion Prediction

Hilmar Bungum

NORSAR, Norway

Independent Reviewer

Ground Motion Prediction

Jack Baker

Stanford University, US

Independent Reviewer

Building Fragility

Julian Bommer

Independent Consultant,
London

Collaborator

Ground Motion Prediction and Site Response

Tijn Berends

Student; University
Groningen

Independent Reviewer

Site Response and Shallow Geological Model

Loes Buijze

University Utrecht

Collaborator

Rock Physics / Core Experiments

Fabrice Cotton

GFZ Potsdam, Germany

Independent Reviewer

Ground Motion Prediction

Helen Crowley

Independent Consultant,
Pavia

Collaborator

Building Fragility and Risk

John Douglas

University of Strathclyde,
UK

Independent Reviewer

Ground Motion Prediction

Ben Edwards

University Liverpool

Collaborator

Ground Motion Prediction

Paolo Franchin

University of Rome “La
Sapienza”

Independent Reviewer

Building Fragility

Damian Grant

ARUP

Collaborator

Building Fragility

Michael Griffith

University of Adelaide,
Australia

Independent Reviewer

Building Fragility

Russell Green

Virginia Tech, USA

Collaborator

Liquefaction Model

Brad Hager

Massachusetts Institute of
Technology

Independent Advisor

Geomechanics

Curt Haselton

California State University,
US

Independent Reviewer

Building Fragility

Rien Herber

University Groningen

Independent Facilitator

General

Rob van der Hilst

Massachusetts Institute of
Technology

Independent Advisor

Geomechanics

Jason Ingham

University of Auckland

Independent Reviewer

Building Fragility

Adriaan Janszen

Exxonmobil

Independent Reviewer

Shallow Geological Model

Mandy Korff

Deltares

Collaborator

Site Response, liquefaction and Shallow
Geological Model

36

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Table continued:

External Expert

Affiliation

Role

Main Expertise Area

Marco de Kleine

Deltares

Collaborator

Site Response and Shallow Geological Model

Pauline Kruiver

Deltares

Collaborator

Site Response and Shallow Geological Model

Florian Lehner

University of Vienna

Independent Reviewer

Rock mechanics

Ger de Lange

Deltares

Collaborator

Site Response and Shallow Geological Model

Nico Luco

United States Geological
Survey

Independent Reviewer

Building Fragility

Eric Meijles

University Groningen

Independent Reviewer

Shallow Geological Model

Guido Magenes

EUCentre Pavia

Collaborator

Building Fragility

Ian Main

University Edinburgh

Independent Reviewer

Seismogenic Model / Statistics

Piet Meijers

Deltares

Collaborator

Site Response, liquefaction and Shallow
Geological Model

Michail Ntinalexis

Independent

Collaborator

Ground Motion Prediction

Barbara Polidoro

Independent Consultant,
London

Collaborator

Ground Motion Prediction

Matt Pickering

Student; Leeds University

Collaborator

Seismic Event Location

Rui Pinho

University Pavia

Collaborator

Building Fragility

Adrian Rodriguez -Marek

Virginia Tech, USA

Collaborator

Site Response Assessment

Emily So

Cambridge Architectural
Research Ltd

Collaborator

Injury model

Robin Spence

Cambridge Architectural
Research Ltd

Collaborator

Injury model

Chris Spiers

University Utrecht

Collaborator

Rock Physics / Core Experiments

Joep Storms

TU Delft

Independent Reviewer

Shallow Geological Model

Jonathan Stewart

UCLA, California, USA

Independent Reviewer

Ground Motion Prediction

Peter Stafford

Imperial College London

Collaborator

Ground Motion Prediction

Peter Styles

Keele University

Independent Advisor

Geomechanics

Tony Taig

TTAC Limited

Collaborator

Risk

Dimitrios Vamvatsikos

NTUA, Greece

Independent Reviewer

Building Fragility

Brecht Wassing

TNO

Collaborator

Geomechanics

37

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Table continued:

External Expert

Affiliation

Role

Main Expertise Area

Ivan Wong

AECOM, Oakland, USA

Independent Reviewer

Ground Motion Prediction

Stefan Wiemer

ETHZ Zurich

Independent Advisor

Geomechanics

Teng Fong Wong

University Hong Kong

Independent Reviewer

Rock mechanics

Bob Youngs

AMEC, Oakland, USA

Independent Reviewer

Ground Motion Prediction

Mark Zoback

Stanford University

Independent Reviewer

Seismological Model and Geomechanics

38

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Appendix C – Hazard Maps for the period 1/1/2015 to 1/1/2017
In the main text of this report (Section Hazard Assessment), the evaluation period for the Hazard and Risk was
set to the 5 years following the submission of the update of the 2016 Winningsplan, i.e. 1-7-2016 to 1-7-2021.
In figure C1 hazard maps are shown for the 2 year period: 1-1-2015 to 1-1-2017. The maps in this figure show
the hazard metric of PGA with a 0.2% / year exceedance chance. Both the hazard maps for a production
scenario of 39.4 Bcm/year and 33 Bcm/year are shown.
For the production scenario of 39.4 Bcm/year the maximum PGA is 0.32 g during the 2 year period 1-1-2015 to
1-1-2017. As comparison for the same production scenario, over the 5 year period 1-7-2016 to 1-7-2021 the
maximum PGA is 0.35 g. The relatively small increase in PGA for the later period is the result of the (1) longer
evaluation duration combined with (2) a shift in the evaluation time period for this non-stationary seismicity
process.

GMPE V1 (Mean) period 1-1-2015 to 1-1-2017

Figure C1

39.4 Bcm/year

33 Bcm/year

Max PGA = 0.32g

Max PGA = 0.31g

Mean hazard map for period 1-1-2015 to 1-1-2017. Production: 39.4 Bcm/year and 33 bcm/year.
Compaction Model: Inversion, Activity Rate: V1, M ≥ 3.5 Metric shown is 0.2% year-1 chance of exceedance
(10% chance in 50 years).

39

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Appendix D – Large format Hazard Maps for better reading
Below figures from the report are shown in a larger format. The figure numbers correspond with the numbers
in the report.
Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 39.4 bcm/year

Max PGA = 0.35 g
Figure 20:

Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 39.4 bcm/year – Compaction:
Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10%
chance in 50 years).

40

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 33 bcm/year

Max PGA = 0.34 g
Figure 22

Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 33 bcm/year – Compaction:
Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10%
chance in 50 years).

Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 21 bcm/year

41

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015

Max PGA = 0.34 g
Figure 22

Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production 21 bcm/year Compaction:
Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10%
chance in 50 years).

42

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production update Winningsplan 2013

Max PGA = 0.43 g
Figure 22

Mean hazard map - period: 1-7-2016 to 1-7- 2021 – Production update Winningsplan 2013 –
Compaction: Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of
exceedance (10% chance in 50 years).

43

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Mean hazard map - period: 1-1-2015 to 1-1- 2017 – Production 39.4 Bcm/year

Max PGA = 0.32 g
Figure C1

Mean hazard map - period: 1-1-2015 to 1-1- 2017 – Production 39.4 bcm/year– Compaction:
Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10%
chance in 50 years).

44

Hazard and Risk Assessment for Induced Seismicity Groningen - Update 1st May 2015
Mean hazard map - period: 1-1-2015 to 1-1- 2017 – Production 33 Bcm/year

Max PGA = 0.31 g
Figure C1

Mean hazard map - period: 1-1-2015 to 1-1- 2017 – Production 33 bcm/year– Compaction:
Inversion - Linear, Activity Rate: V1, M ≥ 3.5 Metric: 0.2%/year chance of exceedance (10%
chance in 50 years).

45