Dike Segment Research Articles

Multiscale Spatial Patterns in Giant Dike Swarms Identified Through Objective Feature Extraction

AbstractDike swarms are ubiquitous on terrestrial planets and represent the frozen remnants of magma transport networks. However, spatial complexity, protracted emplacement history, and uneven surface exposure typically make it difficult to quantify patterns in dike swarms on different scales. In this study, we address this challenge using the Hough transform (HT) to objectively link dissected dike segments and analyze multiscale spatial structure in dike swarms. We apply this method to swarms of three scales: the Spanish Peaks, USA; the Columbia River Flood Basalt Group (CRBG), USA; the Deccan Traps Flood Basalts, India. First, we cluster dike segments in HT space, recognizing prevalent linearly aligned structures that represent single dikes or dike packets, with lengths up to 10 − 30x the mapped mean segment length. Second, we identify colinear and radial dike segment mesoscale structures within each data set, using the HT to segment swarms into constituent spatial patterns. We show that for both the CRBG and Deccan Traps, a single radial or circumferential swarm does not well characterize the data. Instead, multiple and sometimes overlapping mesoscale linear and radial features are prevalent suggesting a complex history of crustal stresses. The HT can provide useful insights in a variety of geologic settings where many quasi‐linear features, at any scale, are superimposed spatially.

Optimal planning of flood defence system reinforcements using a greedy search algorithm

Climate change and deterioration require a continuous effort to reinforce flood defences and meet reliability requirements. To efficiently upgrade flood defence systems, insight in costs and benefits of measures at a system level is required throughout the process of planning and design. Due to the size of flood defence systems the number of possible decisions is large, which hampers system optimization. We describe a greedy search algorithm that can find (near-)optimal combinations of reinforcement measures for dike segments. The algorithm has been validated by comparing results for 2800 different dike segments to an integer programming implementation. The difference in objective value (Total Cost) is only 0.04% on average, which is small compared to other uncertainties in assessment and design of dike segments. The algorithm is applied to a reinforcement project for a dike segment of 41 independent sections, and compared to the common design practice which uses reliability-based requirements on a section level. It is found that the resulting reinforced dike segment is 42% cheaper to construct than the one obtained from the common approach, based on the same input information. This illustrates the practical and societal value of the design approach using a greedy search algorithm in this context.

The Chief Joseph dike swarm of the Columbia River flood basalts, and the legacy data set of William H. Taubeneck

Abstract The Miocene Columbia River Basalt Group (CRBG) is the youngest and best studied continental flood basalt province on Earth. The 210,000 km3 of basaltic lava flows in this province were fed by a series of dike swarms, the largest of which is the Chief Joseph dike swarm (CJDS) exposed in northeastern Oregon and southwestern Washington. We present and augment an extensive data set of field observations, collected by Dr. William H. Taubeneck (1923–2016; Oregon State University, 1955–1983); this data set elucidates the structure of the CJDS in new detail. The large-scale structure of the CJDS, represented by 4279 mapped segments mostly cropping out over an area of 100 × 350 km2, is defined by regions of high dike density, up to ∼5 segments/km−2 with an average width of 8 m and lengths of ∼100–1000 m. The dikes in the CJDS are exposed across a range of paleodepths, from visibly feeding surface flows to ∼2 km in depth at the time of intrusion. Based on extrapolation of outcrops, we estimate the volume of the CJDS dikes to be 2.5 × 102–6 × 104 km3, or between 0.1% and 34% of the known volume of the magma represented by the surface flows fed by these dikes. A dominant NNW dike segment orientation characterizes the swarm. However, prominent sub-trends often crosscut NNW-oriented dikes, suggesting a change in dike orientations that may correspond to magmatically driven stress changes over the duration of swarm emplacement. Near-surface crustal dilation across the swarm is ∼0.5–2.7 km to the E-W and ∼0.2–1.3 km to the N-S across the 100 × 350 km region, resulting in strain across this region of 0.4%–13.0% E-W and 0.04%–0.3% N-S. Host-rock partial melt is rare in the CJDS, suggesting that only a small fraction of dikes were long-lived.

Physically Consistent Modeling of Dike‐Induced Deformation and Seismicity: Application to the 2014 Bárðarbunga Dike, Iceland

AbstractDike intrusions are often associated with surface deformation and propagating swarms of earthquakes. These are understood to be manifestations of the same underlying physical process, although rarely modeled as such. We construct a physics‐based model of the 2014 Bárðarbunga dike, by far the best observed large dike ( 0.5 km ) to date. We constrain the background stress state by the total dike deformation, the time‐dependent dike pressure from continuous GPS and the extent of the seismic swarm, and the spatial dependence of frictional properties via the space‐time evolution of seismicity. We find that the geodetic and earthquake data can be reconciled with a self‐consistent set of parameters. The complex spatial and temporal evolution of the Bárðarbunga seismicity can be explained by dike‐induced elastic stress changes on preexisting faults, constrained by observed focal mechanisms. In particular, the model captures the segmentation of seismicity, where only the newest dike segment is seismically active. Our results indicate that many features of the seismicity result from the interplay between time‐dependent magma pressure within the dike and stress memory effects. The spatial variability in seismicity requires heterogeneity in frictional properties and/or local initial stresses. Modeling suggests that the dike pressure drops during rapid advances and increases during pauses, which primarily causes the segmentation of the seismicity. Joint analysis of multiple data types could potentially lead to improved, physics‐based eruption forecasts.

An Integrated Approach to Flood Risk Management Management and Spatial Quality Enhancement for a Netherlands’ River Polder Area

In the previous paper, the aspect of including interventions from different flood risk safety layers is explained quite concisely. In this publication, an extended approach for the inclusion of interventions from different flood risk layers are described in more detail. The paper demonstrates how the Netherlands’ policy shift from a probability-based flood risk target to a risk-based flood risk target increased the range of interchangeable measures for flood risk protection. Though applying a risk-based mindset, the Netherlands’ flood risk reduction targets were, until recently, defined as probability-based safety standards. This resulted in a uniform dike-ring approach in which different dike-rings have different safety standards, based on, amongst others, the perceived economic value of the area, which are applied uniformly to the whole dike-ring. Within this probability reduction based system it is possible to define interchangeable flood risk management interventions at different locations, for instance, by proposing interventions of different scales, as demonstrated in the previous publication. The ‘Room for the River’ project is an example of providing alternative probability reduction measures, since both dike elevation and load reduction reduce the probability of a flood. However, applying risk-based flood risk targets conceptually considerably extends the amount of interchangeable flood risk measures. Not only does it, next to probability reduction measures, allow for the inclusion of consequence reduction measures (such as flood proofing buildings, elevating areas, and improving evacuation), but compared to the uniform dike-ring approach, it also allows for differentiations in probability standards per dike segment. This conceptually more fine-meshed perspective of the dike-ring extends the amount of variable locations for flood risk management interventions. In the research-by-design study described in this paper, the examined method for the aspect of ‘changing the layer of the flood risk intervention’ is applied to the Albasserwaard case study area. The paper demonstrates how the Netherlands’ recent shift from a probability standard target towards a risk-based target, by increasing the amount of interchangeable flood risk management interventions for the case study area, strengthens the possibility of deploying the developed method and the use of spatial quality as an ex-ante criterion.

An Integrated Approach to Flood Risk Management Management and Spatial Quality Enhancement for a Netherlands’ River Polder Area

In the previous paper, the aspect of including interventions from different flood risk safety layers is explained quite concisely. In this publication, an extended approach for the inclusion of interventions from different flood risk layers are described in more detail. The paper demonstrates how the Netherlands’ policy shift from a probability-based flood risk target to a risk-based flood risk target increased the range of interchangeable measures for flood risk protection. Though applying a risk-based mindset, the Netherlands’ flood risk reduction targets were, until recently, defined as probability-based safety standards. This resulted in a uniform dike-ring approach in which different dike-rings have different safety standards, based on, amongst others, the perceived economic value of the area, which are applied uniformly to the whole dike-ring. Within this probability reduction based system it is possible to define interchangeable flood risk management interventions at different locations, for instance, by proposing interventions of different scales, as demonstrated in the previous publication. The ‘Room for the River’ project is an example of providing alternative probability reduction measures, since both dike elevation and load reduction reduce the probability of a flood. However, applying risk-based flood risk targets conceptually considerably extends the amount of interchangeable flood risk measures. Not only does it, next to probability reduction measures, allow for the inclusion of consequence reduction measures (such as flood proofing buildings, elevating areas, and improving evacuation), but compared to the uniform dike-ring approach, it also allows for differentiations in probability standards per dike segment. This conceptually more fine-meshed perspective of the dike-ring extends the amount of variable locations for flood risk management interventions. In the research-by-design study described in this paper, the examined method for the aspect of ‘changing the layer of the flood risk intervention’ is applied to the Albasserwaard case study area. The paper demonstrates how the Netherlands’ recent shift from a probability standard target towards a risk-based target, by increasing the amount of interchangeable flood risk management interventions for the case study area, strengthens the possibility of deploying the developed method and the use of spatial quality as an ex-ante criterion.

Uncertainty in flood damage estimates and its potential effect on investment decisions

Abstract. This paper addresses the large differences that are found between damage estimates of different flood damage models. It explains how implicit assumptions in flood damage functions and maximum damages can have large effects on flood damage estimates. This explanation is then used to quantify the uncertainty in the damage estimates with a Monte Carlo analysis. The Monte Carlo analysis uses a damage function library with 272 functions from seven different flood damage models. The paper shows that the resulting uncertainties in estimated damages are in the order of magnitude of a factor of 2 to 5. The uncertainty is typically larger for flood events with small water depths and for smaller flood events. The implications of the uncertainty in damage estimates for flood risk management are illustrated by a case study in which the economic optimal investment strategy for a dike segment in the Netherlands is determined. The case study shows that the uncertainty in flood damage estimates can lead to significant over- or under-investments.

Seismic source dynamics of gas‐piston activity at Kı̄lauea Volcano, Hawai‘i

AbstractSince 2008, eruptive activity at the summit of Kı̄lauea Volcano, Hawai‘i has been confined to the new Overlook pit crater within the Halema‘uma‘u Crater. Among the broad range of magmatic processes observed in the new pit are recurring episodes of gas pistoning. The gas‐piston activity is accompanied by seismic signals that are recorded by a broadband network deployed in the summit caldera. We use raw data recorded with this network to model the source mechanism of representative gas‐piston events in a sequence that occurred on 20–25 August 2011 during a gentle inflation of the Kı̄lauea summit. To determine the source centroid location and source mechanism, we minimize the residual error between data and synthetics calculated by the finite difference method for a point source embedded in a homogeneous medium that takes topography into account. We apply a new waveform inversion method that accounts for the contributions from both translation and tilt in horizontal seismograms through the use of Green's functions representing the seismometer response to translation and tilt ground motions. This method enables a robust description of the source mechanism over the period range 1–10,000 s. Most of the seismic wavefield produced by gas‐pistoning originates in a source region ∼1 km below the eastern perimeter of the Halema‘uma‘u pit crater. The observed waveforms are well explained by a simple volumetric source with geometry composed of two intersecting cracks featuring an east striking crack (dike) dipping 80°to the north, intersecting a north striking crack (another dike) dipping 65° to the east. Each gas‐piston event is marked by a similar rapid inflation lasting a few minutes, trailed by a slower deflation ramp extending up to 15 min, attributed to the efficient coupling at the source centroid location of the pressure and momentum changes accompanying the growth and collapse of a layer of foam at the top of the lava column. Assuming a simple lumped parameter representation of the shallow magmatic system, the observed pressure and volume variations can be modeled with the following attributes : foam thickness (10–50 m), foam cell diameter (0.04–0.10 m), and gas‐injection velocity (0.01–0.06 m s−1). Gas‐piston activity occurs in a narrow pipe with diameter of 6 m connecting the Halema‘uma‘u pit crater to the subjacent dike system. The height of the magma column is estimated at ∼104 m at the start of the sequence based on the period of very long period (VLP) oscillations accompanying the onset of the gas‐piston signal. Based on the change in the period of VLP oscillations and tilt evidence, the height of the magma column is inferred to have risen by up to ∼23 m by the end of the 5 day long sequence. A penny‐shaped crack model of the dike geometry yields effective diameters of ∼1.2–2.9 km for the east dike and 0.7 km for the north dike. The shallower north dike segment is embedded in a relatively weak medium, compatible with expected mechanical properties in the hydrothermal environment of this dike.

Shallow conduit system at Kilauea Volcano, Hawaii, revealed by seismic signals associated with degassing bursts

[1] Eruptive activity at the summit of Kilauea Volcano, Hawaii, beginning in March, 2008 and continuing to the present time is characterized by episodic explosive bursts of gas and ash from a vent within Halemaumau Pit Crater. These bursts are accompanied by seismic signals that are well recorded by a broadband network deployed in the summit caldera. We investigate in detail the dimensions and oscillation modes of the source of a representative burst in the 1−10 s band. An extended source is realized by a set of point sources distributed on a grid surrounding the source centroid, where the centroid position and source geometry are fixed from previous modeling of very-long-period (VLP) data in the 10–50 s band. The source time histories of all point sources are obtained simultaneously through waveform inversion carried out in the frequency domain. Short-scale noisy fluctuations of the source time histories between adjacent sources are suppressed with a smoothing constraint, whose strength is determined through a minimization of the Akaike Bayesian Information Criterion (ABIC). Waveform inversions carried out for homogeneous and heterogeneous velocity structures both image a dominant source component in the form of an east trending dike with dimensions of 2.9 × 2.9 km. The dike extends ∼2 km west and ∼0.9 km east of the VLP centroid and spans the depth range 0.2–3.1 km. The source model for a homogeneous velocity structure suggests the dike is hinged at the source centroid where it bends from a strike E 27°N with northern dip of 85° west of the centroid, to a strike E 7°N with northern dip of 80° east of the centroid. The oscillating behavior of the dike is dominated by simple harmonic modes with frequencies ∼0.2 Hz and ∼0.5 Hz, representing the fundamental mode ν11 and first degenerate mode ν12 = ν21 of the dike. Although not strongly supported by data in the 1–10 s band, a north striking dike segment is required for enhanced compatibility with the model elaborated in the 10–50 s band. This dike provides connectivity between the east trending dike and the new vent within Halemaumau Pit Crater. Waveform inversions with a dual-dike model suggest dimensions of 0.7 × 0.7 km to 2.6 × 2.6 km for this segment. Further elaboration of the complex dike system under Halemaumau does not appear to be feasible with presently available data.

Magmatic flow-direction indicators in a giant diabase feeder dike, Connecticut

Recent studies have suggested that many large diabase dikes have been emplaced laterally rather than vertically. These studies report only unidirectional flow, which is usually based on measurements of anisotropy of magnetic susceptibility. However, in the 250-km-long Higganum dike of southern New England (United States), seven independent flow-direction indicators record a complex history of forward- and backward-moving magma. We would expect other similar-size dikes to have had equally complex histories. Measurements within one en echelon segment of the Higganum dike show that as the magma rose, it spread laterally toward the ends of the segment and that backflow was in the reverse direction of the forward flow. The Higganum dike is interpreted to have formed from a linear array of intrusive fingers, each finger spreading laterally to form an en echelon dike segment as it rose through the lithosphere.

Ground motion in the near field of a fluid‐driven crack and its interpretation in the study of shallow volcanic tremor

We present a study of the motion of the ground in the near field of a fluid‐driven tensile crack embedded in a layered half space. The source that we consider is the jerky opening of a channel connecting two fluid‐filled cracks, and the cause of this opening is the excess pressure of fluid in one of the cracks. We make a complete representation of the three components of ground motion in the space, time, and frequency domains and analyze the effects of fluid compressibility, source depth, and medium structure on the ground response. The calculations show the presence of a dominant frequency of motion which depends not only on the source geometry and bulk modulus of the fluid but also on medium characteristics, receiver position, and the component of motion being considered. Using this source model, we view an episode of volcanic tremor as a continuous sequence produced by numerous jerky openings of channels occurring randomly in time along a chain of cracks. Our results are applied to the October 5–6, 1963, east rift eruption of Kilauea volcano, Hawaii, and found to be compatible with available seismic data, suggesting that magma is transported through an ensemble of cracks with the area of 1 × 1 km, each pair of cracks constituting an individual dike segment which opens in discrete increments at a rate of 1/s. We obtain the following parameters for each dike‐segment opening: increase in cavity volume, 40 m3; stress drop, 0.004 bar; seismic moment, 1019 dyn cm; and force applied by the fluid to open the dike, 1014 dyn. The total moment integrated over the entire duration of tremor for the eruption is 0.5 · 1024 dyn cm, roughly equivalent to a single magnitude M = 5 earthquake. The seismic source parameters and other field observations offer constraints on the process of mass transport and are compatible with the excess pressure and viscosity of magma of about 40 bars and 102 P, respectively.