Dike Opening Research Articles

Exploring the link between large earthquakes and magma transport at the onset of the Mayotte volcano-seismic crisis

The archipelago of Comoros was generally considered a moderately seismic region. However, since May 2018, unusual seismicity has been observed off the east coast of Mayotte Island. Following this increase of seismic activity, oceanographic campaigns led to the discovery of a new submarine volcano, indicating that the observed seismicity had a volcanic origin. In this study, we estimate Centroid Moment Tensor (CMT) solutions of M w ≥5 earthquakes of this sequence using 3D Green’s functions and analyze their non-double-couple (non-DC) components. Consistently with previous reports, our results indicate that seismicity migrated upward in May–June 2018 with an increasing number of non-DC events. We show that non-DC components observed in our solutions and previously published catalogs cannot correspond to dike opening or closing as the observed rupture durations suggest unrealistically large magma flow rates. Given that waveforms can be relatively well explained with pure-shear sources, we postulate that non-DC components are most likely artifacts due to unmodeled shallow structural heterogeneities. Most M w ≥5 earthquakes have a strike-slip mechanism consistent with the rupture of pre-existing faults loaded by the regional stress regime and triggered by the increment of stress produced by the upward magma transfer.

Giant dikes and dike-induced seismicity in a weak crust underneath Cerberus Fossae, Mars

Cerberus Fossae is a long and narrow graben system located approximately 1000 km southeast of Elysium Mons, Mars. These structures have long been thought to be dike-induced, and are the focus of renewed attention due to the detection of seismic activity in this area by InSight. Here we report that structural modeling and linear elastic fracture mechanics provide strong evidence that the Cerberus Fossae grabens are dike-related structures, and that their intrusion may have released significant amounts of seismic energy. The modeled dike apertures are between ∼175 and 750 m, and their aspect ratios are consistent with fluid-induced fractures formed in a weakened host rock. We observe densely fractured terrains in high-resolution images of the graben walls, confirming the presence of a weakened crust underneath Cerberus. We used dike geometry and plausible mechanical properties to calculate the source moment released by dike opening and inflation in two scenarios; using the present-day dike dimensions (Md) and in dikes with downscaled sizes to represent smaller intrusions (md). These yielded values between 2.7⋅1016 and 1.3 1021 Nm. From these we estimate that the Cerberus diking events may have expressed seismically through a marsquake series with cumulative moment magnitudes (Mw) between 4.6 and 7.8. InSight has so far detected seismic events with Mw magnitudes as low as 1. Therefore, these results suggest that if the emplacement of even smaller dikes than those inferred below Cerberus is currently taking place, intrusion-induced seismicity could be detected by InSight.

Earthquakes Indicated Stress Field Change During the 2006 Unrest of Augustine Volcano, Alaska

AbstractTo examine controls on the local stress field at Augustine Volcano, Alaska, before its 2006 eruption, we calculated fault plane solutions for volcano‐tectonic earthquakes from 2002 to 2006. The P‐axis orientation was first aligned to the regional maximum compression (NW) and then rotated by about 90° (perpendicular to the dike alignment) after the onset of surface deformation in mid‐August 2005. Using 3D finite element models, we systematically evaluated the effects of tectonic stresses, volcanic edifice densities, and dike overpressures on the local stress field orientation. Combining data and models to generate “phase diagrams” of different stress controls by these competing effects, we argue that moderate tectonic stress of 2–3 MPa at 600 m above sea level slightly exceeded the edifice loading before the precursory deformation and was then overprinted by a local stress field from dike opening with an overpressure of ∼15 MPa.

Magmatic sill formation during dike opening

AbstractThe origin of horizontal magma-filled sills is disputed, particularly for extensional settings where the opening of vertical dikes is the predicted mode of magma intrusion. We simulate long-term extension followed by short-term dike opening in a two-dimensional viscoelastic medium representing a plate spreading center. We show that dike opening in extensionally stressed lithosphere can reduce sublithospheric vertical stresses enough for sill opening given three conditions: (1) the Maxwell time of the asthenosphere is <5× the time interval between dike episodes; (2) the average density of the lithosphere is not much greater than the magma density; and (3) the depth of an axial valley is smaller than a few hundred meters. This mechanism explains the presence of sills along much of the axis of faster-spreading ridges and their absence along slower-spreading centers where thick dense lithosphere and/or sizeable axial valleys exist.

Impacts of Moriyama Dike opening on the water quality in summer at Honjo area, Lake Nakaumi

Impacts of Moriyama Dike opening on the water quality in summer at Honjo area, Lake Nakaumi

Insights Into Mount Etna December 2018 Eruption From Joint Inversion of Deformation and Gravity Data

AbstractWe present results of the joint analysis of ground deformation and superconducting gravity data encompassing Etna's December 2018 eruption. The horizontal ground deformation points to a mechanism of dike opening. Accordingly, we consider forward analytical models describing the effects of a tensile dislocation and use two data inversion approaches, based on heuristic and probabilistic methods. The observed changes can be explained assuming the intrusion of a fluid lighter than bubble‐free magma, along a dike‐like structure. However, the poor fit to the vertical deformation and the discrepancy between bulk volume increase, deduced by the data inversion (some tens of millions of m3), and volume emitted through effusive activity (∼1 × 106 m3) suggest that a more complex mechanism led to the eruption, involving partial inelastic accommodation of the strain and the formation of void space through increase in the fracturing rate of the medium.

Evolution of a lateral dike intrusion revealed by relatively-relocated dike-induced earthquakes: The 2014–15 Bárðarbunga–Holuhraun rifting event, Iceland

Understanding dikes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions, and must be monitored to evaluate volcanic hazard. During the 2014–15 Bárðarbunga rifting event, Iceland, intense seismicity accompanied the intrusion of a ∼50 km lateral dike which culminated in a 6 month long eruption. We here present relocations of earthquakes induced by the lateral dike intrusion, using cross-correlated, sub-sample relative travel times. The ∼100 m spatial resolution achieved reveals the complexity of the dike propagation pathway and dynamics (jerky, segmented), and allows us to address the precise relationship between the dike and seismicity, with direct implications for hazard monitoring. The spatio-temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dike, and following this – after dike opening – indicate a relationship with magma pressure changes (i.e. dike inflation/deflation), followed by a general ‘post-opening’ decay. Seismicity occurs only at the base of the dike, where dike-imposed stresses – combined with the background tectonic stress (from regional extension over >200 yr since last rifting) – are sufficient to induce failure of pre-existing weaknesses in the crust, while the greatest opening is at shallower depths. Emplacement oblique to the spreading ridge resulted in left-lateral shear motion along the distal dike section (studied here), and a prevalence of left-lateral shear failure. Fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters, indicating that they are controlled by the underlying host rock fabric. This high-resolution study provides unprecedented opportunity for comparison with both geodetic and field (frozen dike) observations, and development and consolidation of analytical and analogue models, with implications for rifting processes and real-time monitoring of magma intrusion.

Magmatic controls on axial relief and faulting at mid-ocean ridges

Previous models do not simultaneously reproduce the observed range of axial relief and fault patterns at plate spreading centers. We suggest that this failure is due to the approximation that magmatic dikes open continuously rather than in discrete events. During short – lived events, dikes open not only in the strong axial lithosphere but also some distance into the underlying weaker asthenosphere. Axial valley relief affects the partitioning of magma between the lithosphere and asthenosphere during diking events. The deeper the valley, the more magma goes into lithospheric dikes in each event and so the greater the average opening rate of those dikes. The long-term rate of lithospheric dike opening controls faulting rate and axial depth. The feedback between axial valley depth D and lithospheric dike opening rate allows us to analytically relate steady-state values of D to lithospheric thickness HL and crustal thickness HC. A two-dimensional model numerical model with a fixed axial lithospheric structure illustrates the analytic model implications for axial faulting. The predictions of this new model are broadly consistent with global and segment-scale trends of axial depth and fault patterns with HL and HC.

Rapid dike intrusion into Sakurajima volcano on August 15, 2015, as detected by multi-parameter ground deformation observations

We present observations of ground deformation at Sakurajima in August 2015 and model the deformation using a combination of GNSS, tilt and strain data in order to interpret a rapid deformation event on August 15, 2015. The pattern of horizontal displacement during the period from August 14 to 16, 2015, shows a WNW–ESE extension, which suggests the opening of a dike. Using a genetic algorithm, we obtained the position, dip, strike length, width and opening of a dislocation source based on the combined data. A nearly vertical dike with a NNE–SSW strike was found at a depth of 1.0 km below sea level beneath the Showa crater. The length and width are 2.3 and 0.6 km, respectively, and a dike opening of 1.97 m yields a volume increase of 2.7 × 106 m3. 887 volcano-tectonic (VT) earthquakes beside the dike suggest that the rapid opening of the dike caused an accumulation of strain in the surrounding rocks, and the VT earthquakes were generated to release this strain. Half of the total amount of deformation was concentrated between 10:27 and 11:54 on August 15. It is estimated that the magma intrusion rate was 1 × 106 m3/h during this period. This is 200 times larger than the magma intrusion rate prior to one of the biggest eruptions at the summit crater of Minami-dake on July 24, 2012, and 2200 times larger than the average magma intrusion rate during the period from October 2011 to March 2012. The previous Mogi-type ground deformation is considered to be a process of magma accumulation in preexisting spherical reservoirs. Conversely, the August 2015 event was a dike intrusion and occurred in a different location to the preexisting reservoirs. The direction of the opening of the dike coincides with the T-axes and direction of faults creating a graben structure.

Strike‐slip faulting during the 2014 Bárðarbunga‐Holuhraun dike intrusion, central Iceland

AbstractOver a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano in the northern rift zone, Iceland. It created > 30,000 earthquakes at 5–7 km depth along a 48 km path before erupting on 29 August 2014. The seismicity, which tracked the dike propagation, advanced in short bursts at 0.3–4.7 km/h separated by pauses of up to 81 h. During each surge forward, seismicity behind the dike tip dropped. Moment tensor solutions from the leading edge show exclusively left‐lateral strike‐slip faulting subparallel to the advancing dike tip, releasing accumulated strain deficit in the brittle layer of the rift zone. Behind the leading edge, both left‐ and right‐lateral strike‐slip earthquakes are observed. The lack of non‐double‐couple earthquakes implies that the dike opening was aseismic.

On the mechanisms governing dike arrest: Insight from the 2000 Miyakejima dike injection

Magma stored beneath volcanoes is sometimes transported out of the magma chambers by means of laterally propagating dikes, which can lead to fissure eruptions if they intersect the Earth's surface. The driving force for lateral dike propagation can be a lateral tectonic stress gradient, the stress gradient due to the topographic loads, the overpressure of the magma chamber, or a combination of those forces.The 2000 dike intrusion at Miyakejima volcano, Izu arc, Japan, propagated laterally for about 30 km and stopped in correspondence of a strike-slip system, sub-perpendicular to the dike plane. Then the dike continued to inflate, without further propagation. Abundant seismicity was produced, including five M>6 earthquakes, one of which occurred on the pre-existing fault system close to the tip of the dike, at approximately the time of arrest. It has been proposed that the main cause for the dike arrest was the fault-induced stress.Here we use a boundary element numerical approach to study the interplay between a propagating dike and a pre-stressed strike-slip fault and check the relative role played by dike–fault interaction and topographic loading in arresting the Miyakejima dike. We calibrate the model parameters according to previous estimates of dike opening and fault displacement based on crustal deformation observations. By computing the energy released during the propagation, our model indicates whether the dike will stop at a given location. We find that the stress gradient induced by the topography is needed for an opening distribution along the dike consistent with the observed seismicity, but it cannot explain its arrest at the prescribed location. On the other hand, the interaction of dike with the fault explains the arrest but not the opening distribution. The joint effect of the topographic load and the stress interaction with strike-slip fault is consistent with the observations, provided the pre-existing fault system is pre-loaded with a significant stress, released gradually during the dike–fault interplay.Our results reveal how the mechanical interaction between dikes and faults may affect the propagation of magmatic intrusions in general. This has implications for our understanding of the geometrical arrangement of rift segments and transform faults in Mid Ocean Ridges, and for the interplay between dikes and dike-induced graben systems.

Dike model for the 2012–2013 Tolbachik eruption constrained by satellite radar interferometry observations

Abstract A large dike intrusion and fissure eruption lasting 9 months began on November 27, 2013, beneath the south flank of Tolbachik Volcano, Kamchatka, Russia. The eruption was the most recent at Tolbachik since the Great Tolbachik Eruption from 1975 to 1976. The 2012 eruption was preceded by more than 6 months of seismicity that clustered beneath the east flank of the volcano along a NW–SE trend. Seismicity increased dramatically before the eruption, with propagation of the seismicity from the central volcano conduit in the final hours. We use interferometric synthetic aperture radar (InSAR) to compute relative displacement images (interferograms) for SAR data pairs spanning the eruption. We use satellite SAR data from the Canadian Space Agency's RADARSAT-2 and from the Italian Space Agency's COSMO-SkyMed missions. Data are modeled first through a Markov Chain Monte Carlo solution for a single tensile dislocation (dike). We then use a boundary element method that includes topography to model a distributed dike-opening model. We find the best-fitting dike dips 80° to the WNW with maximum opening of 6–8 m, localized in the near surface and more broadly distributed in distinct regions up to 3 km beneath the surface, which varies from 1 to 2 km elevation for the eruptive fissures. The distribution of dike opening and its correspondence with co-diking seismicity suggests that the dike propagated radially from Tolbachik's central conduit.

「山室真澄, 神谷宏, 石飛裕の論文『沿岸域における人為的改変と自然再生―中海本庄工区の堤防開削を例として』に対するコメント」に対する感想

「山室真澄, 神谷宏, 石飛裕の論文『沿岸域における人為的改変と自然再生―中海本庄工区の堤防開削を例として』に対するコメント」に対する感想

山室真澄，神谷宏，石飛裕の論文「沿岸域における人為的改変と自然再生―中海本庄工区の堤防開削を例として」に対するコメント

山室真澄，神谷宏，石飛裕の論文「沿岸域における人為的改変と自然再生―中海本庄工区の堤防開削を例として」に対するコメント

Time‐dependent dike propagation from joint inversion of seismicity and deformation data

Dike intrusions both deform Earth's surface and induce propagating earthquake swarms. We develop methods to utilize both deformation and seismicity from brittle, volcano‐tectonic earthquakes to image time‐dependent dike propagation. Dieterich's (1994) seismicity‐rate theory is used to relate dike‐induced stress changes to seismicity rate and is combined with elastic Green's functions relating dike opening to deformation. Different space‐time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above/below the dike. In the former, seismicity initiates near the dike's leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows. In the latter, seismicity continues at a decaying rate after the tips pass. We focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time. The method is applied to the 2007 Father's Day intrusion in Kilauea Volcano. Seismicity is concentrated at ∼3 km depth, comparable to geodetic estimates of dike depth, and decays rapidly in time. With lateral propagation only and a vertical dike‐tip line, it is difficult to fit both GPS data and the rapid down‐rift jump in seismicity, suggesting significant vertical propagation. For the events to have occurred below the dike requires a very short aftershock decay time, hence unreasonably high background stressing rate. The rapid decay is better explained if the dike extends somewhat below the seismicity. We suggest that joint inversion is useful for studying the diking process and may allow for improved short‐term eruption forecasts.

New constraints on dike injection and fault slip during the 1975–1984 Krafla rift crisis, NE Iceland

Correlation of KH9 spy and SPOT5 satellite images, airphotos, digital elevation model differencing, electronic distance measurement, and leveling survey data is used to constrain the deformation resulting from the 1975–1984 Krafla rifting crisis. We find that diking typically extends to depths of 5 km, while the dike tops range from 0 km in the caldera region to 3 km at the northern end of the rift. Extension is accommodated by diking at depth and normal faulting in the shallowest crust. In the southern section of the Krafla rift, surface opening is 80% of the dike opening at depth. Over the 70–80 km length of the rift, the average dike opening was 4.3–5.4 m. From these estimates, we calculate the total geodetic moment released over the Krafla rift crisis, 4.4–9.0×1019 Nm, which is an order of magnitude higher than the seismic moment released over the same time period, ~5.8×1018 Nm. The total volume of magma added to the upper crust was 1.1–2.1×109m3. This study highlights how optical image correlation using inexpensive declassified spy satellite and airphotos, combined with simple models of crustal deformation, can provide important constraints on the deformation resulting from past earthquake and volcanic events.

Evolution of dike opening during the March 2011 Kamoamoa fissure eruption, Kīlauea Volcano, Hawai`i

AbstractThe 5–9 March 2011 Kamoamoa fissure eruption along the east rift zone of Kīlauea Volcano, Hawai`i, followed months of pronounced inflation at Kīlauea summit. We examine dike opening during and after the eruption using a comprehensive interferometric synthetic aperture radar (InSAR) data set in combination with continuous GPS data. We solve for distributed dike displacements using a whole Kīlauea model with dilating rift zones and possibly a deep décollement. Modeled surface dike opening increased from nearly 1.5 m to over 2.8 m from the first day to the end of the eruption, in agreement with field observations of surface fracturing. Surface dike opening ceased following the eruption, but subsurface opening in the dike continued into May 2011. Dike volumes increased from 15, to 16, to 21 million cubic meters (MCM) after the first day, eruption end, and 2 months following, respectively. Dike shape is distinctive, with a main limb plunging from the surface to 2–3 km depth in the up‐rift direction toward Kīlauea's summit, and a lesser projection extending in the down‐rift direction toward Pu`u `Ō`ō at 2 km depth. Volume losses beneath Kīlauea summit (1.7 MCM) and Pu`u `Ō`ō (5.6 MCM) crater, relative to dike plus erupted volume (18.3 MCM), yield a dike to source volume ratio of 2.5 that is in the range expected for compressible magma without requiring additional sources. Inflation of Kīlauea's summit in the months before the March 2011 eruption suggests that the Kamoamoa eruption resulted from overpressure of the volcano's magmatic system.

沿岸域における人為的改変と自然再生 — 中海本庄工区の堤防開削を例として

対象水域の地形や構造などが大規模公共工事によって変化している場合，工事以前の状態に戻すことが自然再生にとって不可欠と主張されることが多い．しかし，当該工事から数十年経る間に生じた工事以外の要素も自然環境を改変していることから，地形や構造を戻すことで環境が戻るとは限らない．島根県と鳥取県に位置する中海は，干拓目的で本庄工区と呼ばれる水域が堤防で囲まれ，また中海本湖への海水の出入りは中浦水門を通じる工事が行われた．この堤防の開削は中海を元の状態に戻すことになり本庄工区と中海本湖の貧酸素化を緩和するとの見解と，開削は本庄工区の貧酸素化を強化するとの見解が対立したが，前者の見解を支持するシミュレーション結果が地域住民の気運に合致していたため，事業主体者は開削に踏み切った．本研究の結果により，開削によって本庄工区の貧酸素化は強化したことが確認された．また中海本湖の貧酸素化は工事以前から生じていたことが既報により確認できた．これにより，工事以前の状態に戻すことは必ずしも自然環境の再生につながらず，科学的な根拠に基づかない「分かりやすい主張」には慎重に対処すべきであることが示された．開削によって本庄工区や中海本湖の貧酸素化が緩和するとの自然科学の原理に反し，過去の記録とも矛盾したシミュレーション結果を提示するに至った過程の検証が望まれる．

Deep magma storage at Hekla volcano, Iceland, revealed by InSAR time series analysis

[1] Hekla volcano is one of the most active volcanoes in Iceland. The most recent eruption occurred from 26 February to 8 March 2000 when about 0.19 km3 of magma was erupted. We present deformation data from multitemporal analyses of synthetic aperture radar (SAR) images acquired between 1993 and 2008, focusing on pixels with low-phase variance (using persistent scatterer and small baseline approaches). Prior to and after the 2000 eruption, we find a broad area of inflation around the volcano (radius about 20 km), with satellite line-of-sight (LOS) shortening of up to 5 mm/yr. We interpret this signal as the result of pressure increase in a deep-seated magma chamber, which we model as a spherical source at 14–20 km depth increasing in volume by 0.003–0.02 km3/yr. Within a ∼6 km radius of the summit of the volcano, a LOS lengthening is superimposed on the broad inflation signal, which correlates partly with recent lava flows. We interpret this signal as the result of thermally contracting lava flows, combined with viscoelastic yielding due to the load of the volcano and its lavas. Coeruptive deflation during the 2000 eruption was similar to the cumulative inflation from 1993 to 2000 and is consistent with a spherical magma chamber at 14–18 km depth that decreases in volume by 0.04–0.08 km3. Interferograms spanning the 2000 eruption show a local coeruptive deformation signal near the eruptive fissure. This is consistent with a dike opening from the surface to depths up to 5.8 km with a volume of 0.005–0.006 km3.

Spatiotemporal evolution of dike opening and décollement slip at Kīlauea Volcano, Hawai'i

[1] Rapid changes in ground tilt and GPS positions on Kīlauea Volcano, Hawai'i, are interpreted as resulting from a shallow, two-segment dike intrusion into the east rift zone that began at 1217 UTC (0217 HST) on 17 June 2007 and lasted almost 3 days. As a result of the intrusion, a very small volume of basalt (about 1500 m3) erupted on 19 June. Northward tilt at a coastal tiltmeter, subsidence of south flank GPS sites, southeastward displacements at southwestern flank GPS sites, and a swarm of flank earthquakes suggest that a slow slip event occurred on the decollement beneath Kīlauea's south flank concurrent with the rift intrusion. We use 4 min GPS positions that include estimates of time-dependent tropospheric gradients and ground tilt data to study the spatial and temporal relationships between the two inferred shallow, steeply dipping dike segments extending from the surface to about 2 km depth and decollement slip at 8 km depth. We invert for the temporal evolution of distributed dike opening and decollement slip in independent inversions at each time step using a nonnegative least squares algorithm. On the basis of these inversions, the intrusion occurred in two stages that correspond spatially and temporally with concentrated rift zone seismicity. The dike opening began on the western of the two segments before jumping to the eastern segment, where the majority of opening accumulated. Dike opening preceded the start of decollement slip at an 84% confidence level; the latter is indicated by the onset of northward tilt of a coastal tiltmeter. Displacements at southwest flank GPS sites began about 18 h later and are interpreted as resulting from slow slip on the southwestern flank. Additional constraints on the evolution of the intrusion and decollement slip come from inversion of an Envisat interferogram that spans the intrusion until 0822 UTC on 18 June 2007, combined with GPS and tilt data. This inversion shows that up to 0822 UTC on 18 June, decollement slip is only required in a limited region offshore of Ka'ena Point. A similar inversion of the complete event, which includes GPS and tilt data up to 21 June and a second Envisat interferogram spanning the complete intrusion until 21 June, shows decollement slip spread westward across the south flank. This may suggest westward migration of the decollement slip as the event progressed.