Dziak
Robert P.
Dziak
Robert P.
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PreprintFaulting and hydration of the Juan de Fuca plate system( 2009-04-03) Nedimovic, Mladen R. ; Bohnenstiehl, DelWayne R. ; Carbotte, Suzanne M. ; Canales, J. Pablo ; Dziak, Robert P.Multichannel seismic observations provide the first direct images of crustal scale normal faults within the Juan de Fuca plate system and indicate that brittle deformation extends up to ~200 km seaward of the Cascadia trench. Within the sedimentary layering steeply dipping faults are identified by stratigraphic offsets, with maximum throws of 110±10 m found near the trench. Fault throws diminish both upsection and seaward from the trench. Long-term throw rates are estimated to be 13±2 mm/kyr. Faulted offsets within the sedimentary layering are typically linked to larger offset scarps in the basement topography, suggesting reactivation of the normal fault systems formed at the spreading center. Imaged reflections within the gabbroic igneous crust indicate swallowing fault dips at depth. These reflections require local alteration to produce an impedance contrast, indicating that the imaged fault structures provide pathways for fluid transport and hydration. As the depth extent of imaged faulting within this young and sediment insulated oceanic plate is primarily limited to approximately Moho depths, fault- controlled hydration appears to be largely restricted to crustal levels. If dehydration embrittlement is an important mechanism for triggering intermediate-depth earthquakes within the subducting slab, then the limited occurrence rate and magnitude of intraslab seismicity at the Cascadia margin may in part be explained by the limited amount of water imbedded into the uppermost oceanic mantle prior to subduction. The distribution of submarine earthquakes within the Juan de Fuca plate system indicates that propagator wake areas are likely to be more faulted and therefore more hydrated than other parts of his plate system. However, being largely restricted to crustal levels, this localized increase in hydration generally does not appear to have a measurable effect on the intraslab seismicity along most of the subducted propagator wakes at the Cascadia margin.
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ArticleThe Cascadia Initiative : a sea change In seismological studies of subduction zones(The Oceanography Society, 2014-06) Toomey, Douglas R. ; Allen, Richard M. ; Barclay, Andrew H. ; Bell, Samuel W. ; Bromirski, Peter D. ; Carlson, Richard L. ; Chen, Xiaowei ; Collins, John A. ; Dziak, Robert P. ; Evers, Brent ; Forsyth, Donald W. ; Gerstoft, Peter ; Hooft, Emilie E. E. ; Livelybrooks, Dean ; Lodewyk, Jessica A. ; Luther, Douglas S. ; McGuire, Jeffrey J. ; Schwartz, Susan Y. ; Tolstoy, Maya ; Trehu, Anne M. ; Weirathmueller, Michelle ; Wilcock, William S. D.Increasing public awareness that the Cascadia subduction zone in the Pacific Northwest is capable of great earthquakes (magnitude 9 and greater) motivates the Cascadia Initiative, an ambitious onshore/offshore seismic and geodetic experiment that takes advantage of an amphibious array to study questions ranging from megathrust earthquakes, to volcanic arc structure, to the formation, deformation and hydration of the Juan De Fuca and Gorda Plates. Here, we provide an overview of the Cascadia Initiative, including its primary science objectives, its experimental design and implementation, and a preview of how the resulting data are being used by a diverse and growing scientific community. The Cascadia Initiative also exemplifies how new technology and community-based experiments are opening up frontiers for marine science. The new technology—shielded ocean bottom seismometers—is allowing more routine investigation of the source zone of megathrust earthquakes, which almost exclusively lies offshore and in shallow water. The Cascadia Initiative offers opportunities and accompanying challenges to a rapidly expanding community of those who use ocean bottom seismic data.
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ArticleFlux measurements of explosive degassing using a yearlong hydroacoustic record at an erupting submarine volcano(American Geophysical Union, 2012-11-29) Dziak, Robert P. ; Baker, Edward T. ; Shaw, Alison M. ; Bohnenstiehl, DelWayne R. ; Chadwick, William W. ; Haxel, Joseph H. ; Matsumoto, Haru ; Walker, Sharon L.The output of gas and tephra from volcanoes is an inherently disorganized process that makes reliable flux estimates challenging to obtain. Continuous monitoring of gas flux has been achieved in only a few instances at subaerial volcanoes, but never for submarine volcanoes. Here we use the first sustained (yearlong) hydroacoustic monitoring of an erupting submarine volcano (NW Rota-1, Mariana arc) to make calculations of explosive gas flux from a volcano into the ocean. Bursts of Strombolian explosive degassing at the volcano summit (520 m deep) occurred at 1–2 min intervals during the entire 12-month hydrophone record and commonly exhibited cyclic step-function changes between high and low intensity. Total gas flux calculated from the hydroacoustic record is 5.4 ± 0.6 Tg a−1, where the magmatic gases driving eruptions at NW Rota-1 are primarily H2O, SO2, and CO2. Instantaneous fluxes varied by a factor of ∼100 over the deployment. Using melt inclusion information to estimate the concentration of CO2 in the explosive gases as 6.9 ± 0.7 wt %, we calculate an annual CO2 eruption flux of 0.4 ± 0.1 Tg a−1. This result is within the range of measured CO2 fluxes at continuously erupting subaerial volcanoes, and represents ∼0.2–0.6% of the annual estimated output of CO2from all subaerial arc volcanoes, and ∼0.4–0.6% of the mid-ocean ridge flux. The multiyear eruptive history of NW Rota-1 demonstrates that submarine volcanoes can be significant and sustained sources of CO2 to the shallow ocean.
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ArticleHydrothermal discharge during submarine eruptions : the importance of detection, response, and new technology(The Oceanography Society, 2012-03) Baker, Edward T. ; Chadwick, William W. ; Cowen, James P. ; Dziak, Robert P. ; Rubin, Kenneth H. ; Fornari, Daniel J.Submarine volcanic eruptions and intrusions construct new oceanic crust and build long chains of volcanic islands and vast submarine plateaus. Magmatic events are a primary agent for the transfer of heat, chemicals, and even microbes from the crust to the ocean, but the processes that control these transfers are poorly understood. The 1980s discovery that mid-ocean ridge eruptions are often associated with brief releases of immense volumes of hot fluids ("event plumes") spurred interest in methods for detecting the onset of eruptions or intrusions and for rapidly organizing seagoing response efforts. Since then, some 35 magmatic events have been recognized and responded to on mid-ocean ridges and at seamounts in both volcanic arc and intraplate settings. Field responses at mid-ocean ridges have found that event plumes occur over a wide range of eruption styles and sizes, and thus may be a common consequence of ridge eruptions. The source(s) of event plume fluids are still debated. Eruptions detected at ridges generally have high effusion rates and short durations (hours to days), whereas field responses at arc volcanic cones have found eruptions with very low effusion rates and durations on the scale of years. New approaches to the study of submarine magmatic events include the development of autonomous vehicles for detection and response, and the establishment of permanent seafloor observatories at likely future eruption sites.
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ArticleHydroacoustic monitoring of oceanic spreading centers : past, present, and future(The Oceanography Society, 2012-03) Dziak, Robert P. ; Bohnenstiehl, DelWayne R. ; Smith, Deborah K.Mid-ocean ridge volcanism and extensional faulting are the fundamental processes that lead to the creation and rifting of oceanic crust, yet these events go largely undetected in the deep ocean. Currently, the only means available to observe seafloor-spreading events in real time is via the remote detection of the seismicity generated during faulting or intrusion of magma into brittle oceanic crust. Hydrophones moored in the ocean provide an effective means for detecting these small-magnitude earthquakes, and the use of this technology during the last two decades has facilitated the real-time detection of mid-ocean ridge seafloor eruptions and confirmation of subseafloor microbial ecosystems. As technology evolves and mid-ocean ridge studies move into a new era, we anticipate an expanding network of seismo-acoustic sensors integrated into seafloor fiber-optic cabled observatories, satellite-telemetered surface buoys, and autonomous vehicle platforms.
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ArticleEruptive modes and hiatus of volcanism at West Mata seamount, NE Lau basin : 1996–2012(John Wiley & Sons, 2014-10-31) Embley, Robert W. ; Merle, Susan G. ; Baker, Edward T. ; Rubin, Kenneth H. ; Lupton, John E. ; Resing, Joseph A. ; Dziak, Robert P. ; Lilley, Marvin D. ; Chadwick, William W. ; Shank, Timothy M. ; Greene, Ronald ; Walker, Sharon L. ; Haxel, Joseph H. ; Olson, Eric J. ; Baumberger, TamaraWe present multiple lines of evidence for years to decade-long changes in the location and character of volcanic activity at West Mata seamount in the NE Lau basin over a 16 year period, and a hiatus in summit eruptions from early 2011 to at least September 2012. Boninite lava and pyroclasts were observed erupting from its summit in 2009, and hydroacoustic data from a succession of hydrophones moored nearby show near-continuous eruptive activity from January 2009 to early 2011. Successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996–2012 period reveals a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano's WSW rift zone (WSWRZ). Away from the summit, the volumetrically largest eruption during the observational period occurred between May 2010 and November 2011 at ∼2920 m depth near the base of the WSWRZ. The (nearly) equally long ENE rift zone did not experience any volcanic activity during the 1996–2012 period. The cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank. Water column sensors, analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in September 2012 confirmed that the summit eruption had ceased. Based on the historical eruption rates calculated using the bathymetric differencing technique, the volcano could be as young as several thousand years.
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ArticleEvidence of a recent magma dike intrusion at the slow spreading Lucky Strike segment, Mid-Atlantic Ridge(American Geophysical Union, 2004-12-04) Dziak, Robert P. ; Smith, Deborah K. ; Bohnenstiehl, DelWayne R. ; Fox, Christopher G. ; Desbruyeres, Daniel ; Matsumoto, Haru ; Tolstoy, Maya ; Fornari, Daniel J.Mid-ocean ridge volcanic activity is the fundamental process for creation of ocean crust, yet the dynamics of magma emplacement along the slow spreading Mid-Atlantic Ridge (MAR) are largely unknown. We present acoustical, seismological, and biological evidence of a magmatic dike intrusion at the Lucky Strike segment, the first detected from the deeper sections (>1500 m) of the MAR. The dike caused the largest teleseismic earthquake swarm recorded at Lucky Strike in >20 years of seismic monitoring, and one of the largest ever recorded on the northern MAR. Hydrophone records indicate that the rate of earthquake activity decays in a nontectonic manner and that the onset of the swarm was accompanied by 30 min of broadband (>3 Hz) intrusion tremor, suggesting a volcanic origin. Two submersible investigations of high-temperature vents located at the summit of Lucky Strike Seamount 3 months and 1 year after the swarm showed a significant increase in microbial activity and diffuse venting. This magmatic episode may represent one form of volcanism along the MAR, where highly focused pockets of magma are intruded sporadically into the shallow ocean crust beneath long-lived, discrete volcanic structures recharging preexisting seafloor hydrothermal vents and ecosystems.
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ArticleVolcanic eruptions in the deep sea(The Oceanography Society, 2012-03) Rubin, Kenneth H. ; Soule, Samuel A. ; Chadwick, William W. ; Fornari, Daniel J. ; Clague, David A. ; Embley, Robert W. ; Baker, Edward T. ; Perfit, Michael R. ; Caress, David W. ; Dziak, Robert P.Volcanic eruptions are important events in Earth's cycle of magma generation and crustal construction. Over durations of hours to years, eruptions produce new deposits of lava and/or fragmentary ejecta, transfer heat and magmatic volatiles from Earth's interior to the overlying air or seawater, and significantly modify the landscape and perturb local ecosystems. Today and through most of geological history, the greatest number and volume of volcanic eruptions on Earth have occurred in the deep ocean along mid-ocean ridges, near subduction zones, on oceanic plateaus, and on thousands of mid-plate seamounts. However, deep-sea eruptions (> 500 m depth) are much more difficult to detect and observe than subaerial eruptions, so comparatively little is known about them. Great strides have been made in eruption detection, response speed, and observational detail since the first recognition of a deep submarine eruption at a mid-ocean ridge 25 years ago. Studies of ongoing or recent deep submarine eruptions reveal information about their sizes, durations, frequencies, styles, and environmental impacts. Ultimately, magma formation and accumulation in the upper mantle and crust, plus local tectonic stress fields, dictate when, where, and how often submarine eruptions occur, whereas eruption depth, magma composition, conditions of volatile segregation, and tectonic setting determine submarine eruption style.
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ArticleHydroacoustic monitoring of seafloor spreading and transform faulting in the equatorial Atlantic Ocean(American Geophysical Union, 2022-06-26) Parnell-Turner, Ross ; Smith, Deborah K. ; Dziak, Robert P.Seismicity along mid-ocean ridges and oceanic transform faults provides insights into the processes of crustal accretion and strike-slip deformation. In the equatorial Atlantic ocean, the slow-spreading Mid-Atlantic Ridge is offset by some of the longest-offset transform faults on Earth, which remain relatively poorly understood due to its remote location far from land-based teleseismic receivers. A catalog of T-phase events detected by an array of 10 autonomous hydrophones deployed between 2011 and 2015, extending from 20°N to 10°S is presented. The final catalog of 6,843 events has a magnitude of completeness of 3.3, compared to 4.4 for the International Seismic Center teleseismic catalog covering the same region, and allows investigation of the dual processes of crustal accretion and transform fault slip. The seismicity rate observed at asymmetric spreading segments (those hosting detachment faults) is significantly higher than that of symmetric spreading centers, and 74% of known hydrothermal vents along the equatorial Mid-Atlantic Ridge occur on asymmetric spreading segments. Aseismic patches are present on nearly all equatorial Atlantic transform faults, including on the Romanche transform where regional rotation and transpression could explain both bathymetric uplift and reduction in seismic activity. The observed patterns in seismicity provide insight into the thermal and mechanical structure of the ridge axis and associated transform faults, and potentially provide a method for investigating the distribution of hydrothermal vent systems.