We investigate ground movements induced by the 8 February 2016, Mw=4.2 earthquake at the Los Humeros Geothermal Field (Mexico) using Sentinel-1 radar interferometry. Previous estimated focal mechanism solution based on seismic data with a hypocentral depth of 1900 m could not resolve the measured coseismic surface deformation pattern. In this study, we applied inverse elastic dislocation models to estimate the source parameters of the seismic event. Our models suggest the reverse reactivation of the Los Humeros normal fault at a shallower depth (<1000 m), with a more significant left lateral component below ~400 m depth. The occurrence of such shallow events at Los Humeros pose increased risks for the neighboring communities and infrastructure. Therefore, continuous monitoring of seismicity and cautious planning of field operations are crucial.

A NNW-SSE striking fault swarm, including the Los Humeros fault, acts as a major boundary of the subsiding area observed by InSAR time-series between February 2016 and May 2019. A potential explanation of the reverse reactivation of the Los Humeros fault and following downward movement of the eastern fault block is the depressurization of the whole hydrothermal system. Such depressurization can occur due to the exploitation of the geothermal field and/or due to natural pressure/temperature changes related to magmatic activity.@en

In the Netherlands land subsidence is a continuously ongoing process. Consequently, an increasing number of people and economic assets are exposed to subsidence, damage costs are soaring, and flood risk and greenhouse gas emissions are increasing. In some areas tipping points have already been reached, where current land-use can no longer be maintained without considerable costs, underlining the urgency to take action.

Together with a consortium consisting of universities, research institutes, governmental agencies, public and private partners we have developed a national, multidisciplinary research programme aiming to develop an integrative approach to achieve feasible, legitimate and sustainable solutions for managing the negative societal effects of land subsidence, connecting fundamental research on subsidence processes to socio-economic impact of subsidence and to governance and legal framework design.

The program is designed to co-create insights that help to effectively mitigate and adapt to subsidence within the Netherlands by making major improvements in measuring and modeling the processes and consequences of subsidence, identifying, developing and critically evaluating control measures and designing governance and legal approaches that facilitate their implementation. Hereto we will develop (a) new satellite-based technology to measure, attribute and monitor subsidence, (b) solid understanding of the interacting multiple processes contributing to total subsidence, (c) sophisticated physical and economic numerical models to predict human-induced subsidence rates and impacts, and (d) implementation strategies that go beyond technical measures, to strengthen governance and financing capacities as well as legal frameworks. This fully integrated approach deals with all impacts of land subsidence on society and the economy.@en

Surface deformation due to fluid extraction can be detected by satellite-based geodetic sensors, providing important insights on subsurface geomechanical properties. In this study, we use Differential Interferometric Synthetic Aperture Radar (DInSAR) observations to measure ground deformation due to fluid extraction at the Los Humeros Geothermal Field (Puebla, Mexico). Our main goal is to reveal the pressure distribution in the reservoir and to identify reservoir compartmentalization, which can be important aspects for optimizing the production of the field. The result of the PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) analysis shows that the subsidence at the LHGF was up to 8 mm/year between April 2003 and March 2007, which is small relative to the produced volume of 5×106 m3/year. The subsidence pattern indicates that the geothermal field is controlled by sealing faults separating the reservoir into several blocks. To assess if this is the case, we relate surface movements with volume changes in the reservoir through analytical solutions for different types of nuclei of strain. We constrain our models with the movements of the PS points as target observations. Our models imply small volume changes in the reservoir, and the different nuclei of strain solutions differ only slightly. These findings suggest that the pressure within the reservoir is well supported and that reservoir recharge is taking place.

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Ground surface dynamics is one of the processes influencing the future of the Wadden Sea area. Vertical land movement, both subsidence and heave, is a direct contributor to changes in the relative sea level. It is defined as the change of height of the Earth's surface with respect to a vertical datum. In the Netherlands, The Normaal Amsterdams Peil (NAP) is the official height datum, but its realisation via reference benchmarks is not time-dependent. Consequently, NAP benchmarks are not optimal for monitoring physical processes such as land subsidence. However, surface subsidence can be regarded as a differential signal: The vertical motion of one location relative to the vertical motion of another location. In this case, the actual geodetic height datum is superfluous. In the present paper, we highlight the processes that cause subsidence, with specific focus on the Wadden Sea area. The focus will be toward anthropogenic causes of subsidence, and how to understand them; how to measure and monitor and use these measurements for better characterisation and forecasting; with some details on the activities in the Wadden Sea that are relevant in this respect. This naturally leads to the identification of knowledge gaps and to the formulation of notions for future research.@en

We present first results of PS-InSAR (Persistent Scatterer by Synthetic Aperture Radar Interferometry) time-series over the eastern sector of the Trans-Mexican Volcanic Belt including several volcanic systems. The study area covers the Los Humeros and Acoculco geothermal fields. Los Humeros is one of the largest geothermal fields in Mexico connected to a caldera system that has been active from 0.46 Ma until recent. We performed PS time series analysis using the StaMPS method on Sentinel-1 images acquired between October 2016 and December 2017 to resolve ongoing ground deformation. The Sentinel-1 satellite provides regular observations with fine temporal resolution over large areas, which facilitates detection of satellite line-of-sight surface movements important for monitoring geothermal exploration activities. Generally, the interferograms are of good quality with high coherence even on long time scales. Most of the study area is located at high altitudes (above 2000 m) with strong relief. Asa result, the interferograms seem to be influenced by topography-related atmospheric phase delays, identified by the high correlation between phase and elevation. We correct the topography-related atmospheric phase delays and compare the InSAR estimated displacements with the available GPS data. Our goal is to obtain the deformation associated with ongoing geothermal activities over the Los Humeros geothermal field and other tectonic processes that might be present in the area. Here we present our first results, which will be further extended to estimate volume changes related with the geothermal exploration by inversion methods.@en

This paper reports a study on the use of satellite radar data to constrain the subsurface model parameters of the Bergermeer gas field. Using PSI (Persistent Scatterer InSAR) technology, ascending and descending data were applied in line-of-sight geometry, i.e., without first unravelling the horizontal and vertical components of the signal. The model parameters were constrained using an ensemble smoother with multiple data assimilation. A good match could be obtained with realistic values of the reservoir compaction coefficient and of the subsurface basement elastic modulus. For the aquifer parts that were depleted according to the reservoir simulation, the northern part indeed gave a reasonable value for the compaction coefficient. For the southern part the resulting compaction coefficient was around zero, indicating that the pressure depletion in this part of the aquifer was overestimated and that it was actually not connected to the reservoir. The study shows that it is feasible to use PSI surface movement data to obtain information about the reservoir and that the use of line-of-sight movements from both ascending and descending satellite passes adds an additional dimension to the data and an improved quality of the assimilation results.@en

In an attempt to derive more information on the parameters driving compaction, this paper explores the feasibility of a method utilizing data on compaction-induced subsidence. We commence by using a Bayesian inversion scheme to infer the reservoir compaction from subsidence observations. The method’s strength is that it incorporates all the spatial and temporal correlations imposed by the geology and reservoir data. Subsequently, the contributions of the driving parameters are unravelled. We apply the approach to a synthetic model of an upscaled gas field in the northern Netherlands. We find that the inversion procedure leads to coupling between the driving parameters, as it does not discriminate between the individual contributions to the compaction. The provisional assessment of the parameter values shows that, in order to identify adequate estimate ranges for the driving parameters, a proper parameter estimation procedure (Markov Chain Monte Carlo, data assimilation) is necessary.@en

The surface movement in the Krimpenerwaard polder in The Netherlands results from primary or hydrodynamic settlement/swelling, secondary or creep settlement/swelling, and peat oxidation. We used surface movement measurements in a Bayesian inversion scheme to disentangle the contribution of these three processes to the subsidence. The prior information, including spatial correlations, appeared to be crucial in our procedure. This prior information was derived from geological modeling incorporating the most important uncertainties. The inversion procedure allowed us to quantify the contributions of the three processes with unprecedented accuracy. Surface rise in the data was related to swelling of the clay layers, even though swelling was considered infeasible in the prior information. Despite this, the irreversible nature of peat oxidation was preserved. The improved subsurface description offers prospects for identification of incorrect information and for better assessments of the effects of water management.@en

Understanding and predicting surface movement is important both technically and for social reasons. The shallow processes contributing to subsidence include construction works, peat oxidation, clay compaction, and groundwater withdrawal; deep causes are hydrocarbon and salt production. We describe an inversion procedure we have devised to disentangle the deep and shallow causes of surface movement. It employs a Bayesian inversion scheme, using forward models and other ‘a priori’ information about shallow and deep compaction. Parameter estimation thus takes place at two different depths, thereby disentangling the deep and shallow compaction processes responsible for surface movement. The uncertainty in the surface measurements and ‘a priori’ estimates is naturally incorporated. Furthermore, spatial and temporal correlations can be taken into account through inclusion of the covariance matrix. The inversion scheme is demonstrated for two synthetic cases. The first combines a compacting gas field and a compacting shallow peat layer. We demonstrate that assumptions on the shape of the subsidence bowl are not necessary. We also show how neglecting either deep or shallow causes of subsidence can produce spurious results. The advantage of using the ‘a priori’ estimates of the compaction and the covariance matrix obtained by Monte Carlo simulations is demonstrated with a second synthetic example involving two polders and different depths of their water table. A robust solution is obtained for each polder unit, while a simpler (and faster) ‘a priori’ estimate based on the expected average clay thickness fails to reproduce the actual compaction. Monte Carlo simulations can also be applied to compaction in depleting gas reservoirs. Information on spatial correlations is often available, even when the absolute values of the ‘a priori’ compaction data are quite uncertain. Explicitly incorporating such ‘a priori’ known spatial correlations improves the result significantly.@en

We introduce a novel, time-dependent inversion scheme for resolving temporal reservoir pressure drop from surface subsidence observations (from leveling or GPS data, InSAR, tiltmeter monitoring) in a single procedure. The theory is able to accommodate both the absence of surface subsidence estimates at sites at one or more epochs as well as the introduction of new sites at any arbitrary epoch. Thus, all observation sites with measurements from at least two epochs are utilized. The method uses both the prior model covariance matrix and the data covariance matrix, which incorporates the spatial and temporal correlations between model parameters and data, respectively. The incorporation of the model covariance implicitly guarantees smoothness of the model estimate, while maintaining specific geological features like sharp boundaries. Taking these relations into account through the model covariance matrix enhances the influence of the data on the inverted model estimate. This leads to a better defined and interpretable model estimate. The time-dependent aspect of the method yields a better constrained model estimate and makes it possible to identify non-linear acceleration or delay in reservoir compaction. The method is validated by a synthetic case study based on an existing gas reservoir with a highly variable transmissibility at the free water level. The prior model covariance matrix is based on a Monte Carlo simulation of the geological uncertainty in the transmissibility.@en

Surface subsidence can have major repercussions. A classic example is the seabed above the Ekofisk field, offshore Norway, where excessive subsidence made it necessary to raise the drilling platform by 6 m in the 1980s. On land, subsidence may significantly increase the risk of damage to buildings and infrastructure. But, there is more to say about subsidence. Observations of subsidence can also give us a better handle on the subsurface processes like compaction behaviour of a reservoir, and can tell us more about the reservoir itself: about undrained compartments or the strength of the aquifer. However, to get the information from subsidence data, you have to carefully follow an inver-sion procedure. This inversion exercise is a big challenge, in which all the available knowledge has to be used to the fullest possible extent. In this article we report on the work we have recently performed in this area. @en