Niels Grobbe

• Ph.D.
• Affiliate Faculty Member at University of Hawaiʻi at Mānoa

Deep geothermal energy (~3-6 km depth) is a candidate for sustainable and carbon-free energy supply. One of the main concerns of deep geothermal systems is induced seismicity that may produce earthquakes of economic concerns, challenging the development of this form of alternative energy. So far, cold water injection has been overlooked but may con...

Detection of seismicity is often done using P-wave onsets. To assess detection and localization capabilities of existing and future network configurations, there is a need for relations that predict the expected amplitudes: P-wave ground-motion prediction equations. We derive two equations specifically for upper crustal seismicity. One relation is...

For induced seismicity, the non-stationary, heterogeneous character of subsurface stress perturbations can be a source of spatiotemporal variations in the scaling of event sizes; one of the critical parameters controlling seismic hazard and risk. We demonstrate and test a systematic, statistical, penalized-likelihood approach to analysing both spat...

In the context of our growing population, new paradigms are required for, e.g., the monitoring and management of infrastructure and buildings and the use of the subsurface and its resources. Increasing energy demands entail continuous improvement of imaging techniques to better understand subsurface resources and to maximize production in an enviro...

Geothermal power plant operations circulate large amounts of fluid through the subsurface, but during the exploration phase, we typically have poor understanding of subsurface fluid transportation dynamics at reservoir depths. Being able to identify pre-existing water-filled fracture networks greatly helps to assess geothermal resources and targets...

Key Takeaways Groundwater contamination following a 1977 chemical spill on the Hawaiian island of Oahu caused alarm and led to swift action in the early 1980s, including closure of several drinking water wells. Legislation and other efforts to remediate and monitor the contamination have been rigorous and nearly continuous. Decades later, a recent...

The induced seismicity in the Groningen gas field, The Netherlands, presents contrasted spatio-temporal patterns between the central area and the south west area. Understanding the origin of this contrast requires a thorough assessment of two factors: (1) the stress development on the Groningen faults, and (2) the frictional response of the faults...

We study a watershed containing an old stream valley at the Kaiwi Coast on Oʻahu, Hawaiʻi. The study site has undergone significant hydrogeological changes throughout its history, and at present displays complex interactions of a variety of geological formations. We highlight an innovative and efficient combination of two hydrogeophysical methodolo...

The induced seismicity in the Groningen gas field, The Netherlands, presents contrasted spatio-temporal patterns between the central area and the south west area. Understanding the origin of this contrast requires a thorough assessment of two factors: (1) the stress development on the Groningen faults, and (2) the frictional response of the faults...

We study seismoelectric (SE) surface-wave signals and find that they can be used to infer changes in the SE coupling properties at depth. Seismoelectric surface-wave signals have much higher amplitudes than seismoelectric body-wave signals. We propose to measure both the seismic and the electrical potential or electromagnetic (EM) field along the s...

We propose a comprehensive methodology for the acquisition and processing of self-potential (SP) data, as well as some keys to the interpretation of the results. The wide applicability of the SP method, and its low cost, make it a popular method for use in a variety of natural environments. Despite its versatility and the fact that various publishe...

We present the governing equations describing coupled seismo‐electromagnetic wave propagation in porous media, based on Pride's assumptions. We start with the theory for fully saturated porous media, and reorganize the set of equations to allow for analytically based layered‐Earth numerical modeling. We also present alternative seismoelectric equat...

In this chapter, we discuss the microscale origin of coupled seismo‐electromagnetic fields. We introduce the electrical double layer (EDL) and important electrokinetic processes that take place in porous materials that have a certain degree of pore‐fluid saturation. The electrical double layer at the microscale plays a crucial role in the seismoele...

We demonstrate the value of using the self-potential method to study volcanic environments, and particularly fluid flow in those environments. We showcase the fact that self-potential measurements are a highly efficient way to map large areas of volcanic systems under challenging terrain conditions, where other geophysical techniques may be challen...

Near-surface geophysics has been a part of SEG for decades, but it was not until the end of 2014 that a near-surface group was formally established within the Society. In the few years since then, this group, now known as the SEG Near-Surface Geophysics Technical Section (NSTS, https://www.seg.org/ns ), has expanded its membership, broadened its ac...

Electrical conductivity tomography is a well-established galvanometric method for imaging the subsurface electrical conductivity distribution. We characterize the conductivity distribution of a set of volcanic structures that are different in terms of activity and morphology. For that purpose, we developed a large-scale inversion code named ECT-3D...

In this thesis, I study coupled poroelastic waves and electromagnetic fields in layered media. The focus is two-fold:1. Increase the theoretical and physical understanding of the seismo-electromagnetic phenomenon by analytically-based numerical modeling.2. Investigate the potential of seismo-electromagnetic interferometry.After presenting the gover...

We here explore the application of interferometric principles to the coupled seismo-electromagnetic system. We consider 2D homogeneous space scenarios, and focus on one of the two seismo-electromagnetic propagation modes, the SH-TE mode, where horizontally polarized shear-waves are coupled to the transverse electric mode. We start by presenting the...

We study the accuracy and numerical stability of three eigenvector sets for modelling the coupled poroelastic and electromagnetic layered-Earth response.We use a known eigenvector set, its flux-normalized version and a newly derived flux-normalized set. The new set is chosen such that the system is properly uncoupled when the coupling between the p...

We study if nature can help us overcome the very low signal-to-noise ratio of seismo-electromagnetic converted fields by investigating the effects of thin-bed geological structures on the seismo-electromagnetic signal. To investigate the effects of bed-thinning on the seismo-electromagnetic interference patterns, we numerically simulate seismo-elec...

For multi-parameter problems, such as the seismoelectric system, sensitivity analysis through resolution functions is a low-cost, fast method of determining whether measured fields are sensitive to certain subsurface parameters. We define a seismoelectric resolution function for the inversion of a bulk density perturbation. The synthetic data and G...

The seismoelectric effect is a very interesting and complex physical phenomenon, dealing with the subsurface coupling between mechanical poroelastic wavefields and electromagnetic diffusive fields. Therefore, the seismoelectric method can provide us with both seismic resolution and electromagnetic sensitivity at the same time. In addition, several...

When a mechanical wavefield propagates through a porous, fluid-filled medium, a complex physical phenomenon called the seismoelectric effect can occur. Due to the presence of an electrical double layer at the microscale, coupling between the mechanical wavefield and electromagnetic fields can occur. Pride (1994) has developed a set of governing equ...

Wavefield decomposition forms an important ingredient of various geophysical methods. An example of wavefield decomposition is the decomposition into upgoing and downgoing wavefields and simultaneous decomposition into different wave/field types. The multi-component field decomposition scheme makes use of the recordings of different field quantitie...

The seismoelectric effect where acoustic/seismic waves are converted into electromagnetic waves and vice versa, is of importance for hydrocarbon exploration as it is complementary to the conventional seismic surveys. Also for the detection of orebodies (for example massive sulfides), seismoelectric techniques are promising. For hydrological purpose...

The seismoelectric effect might help improving our knowledge of the subsurface. This complex physical phenomenon can be described by Biot's poroelasticity equations coupled to Maxwell's electromagnetic equations. Besides simultaneously offering seismic resolution and electromagnetic sensitivity, the coefficient coupling these two types of fields ca...

The theory of coupled elastic waves and electromagnetic fields in porous media exists for two decades. Several modeling codes have been developed and some field work has been carried out with mixed success. Modeling the so-called electroseismic and seismo-electromagnetic wavefields is tricky because of the strong elastic fields generated by mechani...

Increasing industrial and societal challenges demand a contin-uous need for improved imaging methods. In recent years, quite some research has been performed on using seismoelec-tric phenomena for geophysical exploration and imaging. Like the other methods, the seismoelectric technique also has its drawbacks. Besides the fact that the physical phen...

The seismoelectric effect can be of importance for hydrocarbon exploration as it is complementary to conventional seismics. Besides enabling seismic resolution and electromagnetic sensitivity at the same time, the seismoelectric method can also provide us with additional, high-value information like porosity and permeability. However, very little i...

Separation of recorded wavefields into downgoing and upgoing constituents is a technique that is used in many geophysical methods. The conventional, multi-component (MC) wavefield decomposition scheme makes use of different recorded wavefield components. In recent years, land acquisition designs have emerged that make use of shallow horizontal down...

We designed and developed an experimental setup in which acoustic to electromagnetic (EM) wave conversions at interfaces can be measured. Theoretical results are obtained with an electrokinetic full-waveform theoretical model, where use was made of the Sommerfeld approach. Using bimodal samples, different fluid–solid interface effects and saturatin...

We present a new approach to apply wavefield decomposition, illustrated for an energy flux-normalized elastodynamic case. We start by considering a situation where two horizontal boreholes are closely separated from each other. By recording only the particle velocities at both depth levels (for example with conventional 3-component geophones) and e...

We have developed an analytically based, energy fluxnormalized numerical modeling code (ESSEMOD), capable of modeling the wave propagation of all existing ElectroSeismic and SeismoElectric source-receiver combinations in horizontally layered configurations. We compare the results of several of these modeled source-receiver combinations in a homogen...

We present a novel method to transform seismic data with sources at the surface and receivers above and below a selected target zone in the subsurface into virtual data with sources and receivers located at the initial receiver locations. The method is based on inverting a series of multidimensional equations of the convolution- and the correlation...

We experimentally validate a relatively recent electrokinetic formulation of the streaming potential (SP) coefficient as developed by Pride (1994). The start of our investigation focuses on the streaming potential coefficient, which gives rise to the coupling of mechanical and electromagnetic fields. It is found that the theoretical amplitude value...

ESSEMOD - Electroseismic and Seismoelectric Flux-Normalized Modeling for Horizontally Layered, Radially Symmetric Configurations

Electrokinetic Fields and Waves: Theory, Experiments and Numerical Modeling

To put constraints on the crustal and upper-mantle structure, seismologists have often made use of the sensitivity of surface wave dispersion observations and teleseismic P-wave receiver functions to the shear velocity structure of the medium. Both types of datasets have their own limitations in resolution. In this study, it was investigated if the...