Seismicity and structure of a magmatic accretionary centre at an ultraslow spreading ridge: The volcanic centre at 85°E/85°N, Gakkel Ridge

Mid-ocean ridges are divergent plate boundaries. Yet, there are important differences between these individual ridges, which seem to be linked to the rate with which they spread apart. The appearance of 'ultraslow' spreading ridges is drastically different from faster spreading ridges. Yet, only few surveys have so far been conducted. In 1999, an exceptional earthquake sequence was teleseismically registered. It was unusual in the magnitudes involved, the number of events registered, and the duration of activity (9 months). It originated at 85°E/85°N at a volcanic centre in the eastern part of Gakkel Ridge. I analyzed this sequence, relocating the entire teleseismic earthquake sequence with three different localization algorithms. I also analyzed a 16-day local dataset which had been collected in 2007, using seismometer arrays installed on ice floes which drifted over the survey area. It shows the seismological aftermath of the spreading episode of 1999 at Gakkel Ridge, resultin in the first local earthquake tomography ever done at an ultraslow spreading centre

On the evolution of elastic properties during laboratory stick-slip experiments spanning the transition from slow slip to dynamic rupture

The physical mechanisms governing slow earthquakes remain unknown, as does the relationship between slow and regular earthquakes. To investigate the mechanism(s) of slow earthquakes and related quasi-dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration. We reproduced the full spectrum of slip behavior, from slow to fast stick slip, by altering the elastic stiffness of the loading apparatus (k) to match the critical rheologic stiffness of fault gouge (kc). Our experiments show an evolution from stable sliding, when k>kc, to quasi-dynamic transients when k ~ kc, to dynamic instabilities when k<kc. To evaluate the microphysical processes of fault weakening we monitored variations of elastic properties. We find systematic changes in P wave velocity (Vp) for laboratory seismic cycles. During the coseismic stress drop, seismic velocity drops abruptly, consistent with observations on natural faults. In the preparatory phase preceding failure, we find that accelerated fault creep causes a Vp reduction for the complete spectrum of slip behaviors. Our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults, depending on frictional properties. In agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by Vp changes during the seismic cycle. The observed reduction in Vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high-resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

Internet of things for disaster management: state-of-the-art and prospects

Disastrous events are cordially involved with the momentum of nature. As such mishaps have been showing off own mastery, situations have gone beyond the control of human resistive mechanisms far ago. Fortunately, several technologies are in service to gain affirmative knowledge and analysis of a disaster's occurrence. Recently, Internet of Things (IoT) paradigm has opened a promising door toward catering of multitude problems related to agriculture, industry, security, and medicine due to its attractive features, such as heterogeneity, interoperability, light-weight, and flexibility. This paper surveys existing approaches to encounter the relevant issues with disasters, such as early warning, notification, data analytics, knowledge aggregation, remote monitoring, real-time analytics, and victim localization. Simultaneous interventions with IoT are also given utmost importance while presenting these facts. A comprehensive discussion on the state-of-the-art scenarios to handle disastrous events is presented. Furthermore, IoT-supported protocols and market-ready deployable products are summarized to address these issues. Finally, this survey highlights open challenges and research trends in IoT-enabled disaster management systems. © 2013 IEEE

Joint document concerning geological studies from 1971 - 1975

In 1971, a joint Soviet-Americam Working Group on Remote Sensing of the Natural Environment was established. It was organized into a number of discipline panels, one of which was on geology. Membership on this panel came from the Geological Survey of the United States and from the Institute of Geology of the U.S.S.R. Academy of Sciences and Ministry Geology of the U.S.S.R.. During the period 1971-1975, this panel conducted coordinated research in the use of space remote sensing data in the field of geology. A summary of that coordinated research effort is presented

Continental breakup and UHP rock exhumation in action: GPS results from the Woodlark Rift, Papua New Guinea

We show results from a network of campaign Global Positioning System (GPS) sites in the Woodlark Rift, southeastern Papua New Guinea, in a transition from seafloor spreading to continental rifting. GPS velocities indicate anticlockwise rotation (at 2–2.7°/Myr, relative to Australia) of crustal blocks north of the rift, producing 10–15 mm/yr of extension in the continental rift, increasing to 20–40 mm/yr of seafloor spreading at the Woodlark Spreading Center. Extension in the continental rift is distributed among multiple structures. These data demonstrate that low-angle normal faults in the continents, such as the Mai'iu Fault, can slip at high rates nearing 10 mm/yr. Extensional deformation observed in the D'Entrecasteaux Islands, the site of the world's only actively exhuming Ultra-High Pressure (UHP) rock terrane, supports the idea that extensional processes play a critical role in UHP rock exhumation. GPS data do not require significant interseismic coupling on faults in the region, suggesting that much of the deformation may be aseismic. Westward transfer of deformation from the Woodlark Spreading Center to the main plate boundary fault in the continental rift (the Mai'iu fault) is accommodated by clockwise rotation of a tectonic block beneath Goodenough Bay, and by dextral strike slip on transfer faults within (and surrounding) Normanby Island. Contemporary extension rates in the Woodlark Spreading Center are 30–50% slower than those from seafloor spreading-derived magnetic anomalies. The 0.5 Ma to present seafloor spreading estimates for the Woodlark Basin may be overestimated, and a reevaluation of these data in the context of the GPS rates is warranted

Analysis of tremor at the San Andreas Fault at Parkfield

Emergent phase arrivals, low amplitude waveforms, and variable event durations make detection and location of tectonic tremor a non-trivial task. In this work I employ a new method to identify tremor in large datasets using a semi-automated technique, which is comprised of an envelope cross-correlation and a Self-Organizing Map (SOM) algorithm to identify and classify event types. Furthermore, I present a new tremor localization method based on time-reversal imaging techniques

Combining experimental volcanology, petrology and geophysical monitoring techniques

In general, an understanding of the complex processes acting before and during volcanic eruptions is approached from various different sides, e.g. laboratory experiments on fragmentation and/or bubble burst eruption mechanisms, petrological analysis of the eruptive products and various geophysical monitoring and source localization techniques. Each of these techniques can deliver valuable insights by adding pieces of information about the physical processes that drive the volcanic activity. However, often studies are focussing on a single aspect of the process, without setting the results in a more general context. Often, this strategy is absolutely valid, when the focus is laid on a single piece in the complex chain of processes taking place in volcanic eruptions. This must fail when the results aim to suggest a valid model for the combined observations at volcanoes using the above described techniques. The resulting models of volcanic source mechanisms and eruptive features can therefore lead to biased assumptions. This study aims to close this gap between laboratory experiments, petro-chemical analysis and modern geophysical monitoring and source localization techniques in a case study of Mt. Yasur (Vanuatu) volcano. The presented laboratory experiments on explosive volcanic eruptions upon rapid decompression show that decompression rate is the dening parameter in the experiments and that a scaling to large-scale processes is valid. Furthermore, a model is presented that correlates measured particle velocities to decompression rate and initial gas-overpressure. This model is used to estimate source volumes and overpressures at Volcan de Colima (Mexico) and Mt. Yasur (Vanuatu). A petrographically and geochemically characterization of Mt. Yasurs eruptive products suggests a shallow magma-mingling process at both of Mt. Yasurs active craters, perhaps due to rejuvenation of material slumped from the crater walls into an open conduit system. A study on the time-reversal imaging technique and its ability to detect the details of finite rupture (or time-variant) processes shows that the limitations of TR imaging start where the source stops being point-localised with respect to the used wavelength. Inversion of the source mechanisms of Strombolian explosions at Mt. Yasur are performed using a multi-parameter dataset consisting of seismic, acoustic and Doppler-radar data. Time-reversal imaging and moment tensor inversion are used to invert the source location of the seismic long-period (f < 1Hz) signals, which is supposed to refl ect fluid movement at depth. The source is located in the north-east of the crater region in a depth of several hundred meters. Furthermore, the source volume of the radiated infrasound signals is estimated from fundamental resonance frequencies. The results showed that the maximum particle velocity measured with the Doppler radar correlates nicely with the estimated source volumes lengths. The inverted seismic moment does not show any correlation with the estimated slug sizes, i.e. the slug size does not map in seismic moment. This is an important information, as it states that a larger source volume does not necessarily produces a larger seismic moment. From these combined results, a common feeder system for all active craters at Mt. Yasur is proposed. The differences in event recurrence rate at the three active craters are believed to be controlled by either the conduit geometry or variations in degassing or cooling rate. Strombolian-type eruptions at Mt. Yasur are suggested to be due to the burst of gas slugs with lengths and overpressures comparable to volcanoes showing similar eruptive patterns. The results illustrate the importance of combined studies that overcome the limitations of single disciplines. In this way, a more comprehensive view of volcanic eruptions and the associated observations is possible. Such a multi-disciplinary approach will contribute to a better understanding of volcanic processes and the associated hazards

Seismicity of ultraslow spreading mid-ocean ridges at local, regional and teleseismic scales: A case study of contrasting segments

The main representatives of ultraslow spreading ridges are the Arctic Ridge System (ARS) and the Southwest Indian Ridge (SWIR). As earthquakes indicate active crustal accretion, monitoring the seismicity provides information about the mechanical state of the lithosphere. The Lena Trough, part of the ARS, spreads obliquely and amagmatic. I relocalized the globally detected earthquakes to show the spatial distribution of the seismicity along the rift axis. During two surveys, our working group recorded the microseismicity of Lena Trough with seismic arrays deployed on ice floes. The second case study concerns the magmatic Orthogonal Supersegment of the SWIR. I accessed the regional dataset of the Neumayer seismic array in Antarctica lying in a distance of ~2100 km to the study area. The dataset contains 743 earthquakes and clearly shows four swarms occurring at an assumed volcanic centre. The new datasets allow a comprehensive evaluation lowering the detection threshold compared to the global station network. Active accretion episodes can be monitored in greater detail showing the spreading mechanisms at contrasting amagmatic and magmatic ridge segments

Local earthquake tomography of Central America : structural variations and fluid transport in the Nicaragua-Costa Rica subduction zone

The Central American convergent margin is characterized by pronounced lateral changes from north to south such as a decreasing dip of the slab, a decreasing magma production and a shift in the volcanic front. To investigate this transition in terms of seismicity and tectonics, a joint on- and offshore local earthquake tomography and P-wave anisotropy studies were performed in central Costa Rica and in S Nicaragua/N Costa Rica respectively. In central Costa Rica, seismic travel time data sets of three on- and off-shore seismic networks were combined for a simultaneous inversion of hypocenter locations, 3-D structure of P-wave velocity and Vp/Vs ratio. The tomographic inversion was performed using about 2000 high quality events. The seismicity and slab geometry as well as Vp and Vp/Vs show significant lateral variation along the subduction zone corresponding to the changes of the incoming plate which consists of serpentinized oceanic lithosphere in the NW, a seamount province in the center and the subducting Coscos Ridge in the SE of the investigation area. Three prominent features can be identified in the Vp and Vp/Vs tomograms: a high velocity zone with a perturbation of 4-10 % representing the subducting slab, a low velocity zone (10-20 %) in the forearc probably caused by deformation, fluid release and hydration, and a low-velocity zone below the volcanic arc related to upwelling fluids and magma. Unlike previously suggested, the dip of the subducting slab does not decrease to the south. Instead, an average steepening of the plate interface from 30° to 45° is observed from north to south and a transition from a plane to a stair-shape plate interface. This is connected with a change in the deformation style of the overriding plate where roughly planar, partly conjugated, clusters of seismicity of regionally varying dip are observed. It could be shown that the Costa Rica Deformation Belt represents a deep crustal transition zone extending from the surface down to 40 km depth. This transition zone indicates the lateral termination of the active part of the volcanic chain and seems to be connected with the changing structure of the incoming plate as well. In S Nicaragua/N Costa Rica, the same inversion procedure was performed using 860 events. The analysis shows low S-wave velocities (~4 km/s), high Vp/Vs ratios (~ 2.0) and an aseismic gap in the upper mantle along the Sandino Basin. These findings are intrepereted as an indication of mantle wedge hydration. The existence of a hydrated forearc upper-mantle wedge in southern Nicaragua and the absence of it in northern Costa Rica is important to understand the variations in the tectonic structures along the margin and provides an improved view of the deep dehydration process in subduction zones. The sharp transition between the Nicaraguan and northern Costa Rican margins is explained by the dominating extensional forces in the southern Nicaraguan overriding plate. In addition to the velocity inversion, a P-wave anisotropy study was performed to have a better understanding in the mantle dynamics and tectonics of the Earth's interior. P-wave anisotropy results show two main structures: 1) Trench-perpendicular seismically fast directions in the incoming plate which can be explained either by the initial mineral orientation at the mid-oceanic ridge or by the deformation parallel to the subduction direction. 2) Trench-parallel seismically fast directions and abrupt rotations to trench-parallel anisotropy in the forearc which support the mantle escape towards to northwest. These patterns of seismic anisotropy may be caused by the olivine fabric transition from A-type to B-type or three dimensional flow associated with along-strike variations in slab geometry