Sharon Kedar

Waveform inversion of very long period impulsive signals associated with magmatic injection beneath Kilauea volcano, Hawaii

We use data from broadband seismometers deployed around the summit of Kilauea Volcano to quantify the mechanism associated with a transient in the flow of magma feeding the east rift eruption of the volcano. The transient is marked by rapid inflation of the Kilauea summit peaking at 22 μrad 4.5 hours after the event onset, followed by slow deflation over a period of 3 days. Superimposed on the summit inflation is a series of sawtooth displacement pulses, each characterized by a sudden drop in amplitude lasting 5–10 s followed by an exponential recovery lasting 1–3 min. The sawtooth waveforms display almost identical shapes, suggesting a process involving the repeated activation of a fixed source. The particle motion associated with each sawtooth is almost linear, and its major swing shows compressional motion at all stations. Analyses of semblance and particle motion are consistent with a point source located 1 km beneath the northeast edge of the Halemaumau pit crater. To estimate the source mechanism, we apply a moment tensor inversion to the waveform data, assuming a point source embedded in a homogeneous half-space with compressional and shear wave velocities representative of the average medium properties at shallow depth under Kilauea. Synthetic waveforms are constructed by a superposition of impulse responses for six moment tensor components and three single force components. The origin times of individual impulses are distributed along the time axis at appropriately small, equal intervals, and their amplitudes are determined by least squares. In this inversion, the source time functions of the six tensor and three force components are determined simultaneously. We confirm the accuracy of the inversion method through a series of numerical tests. The results from the inversion show that the waveform data are well explained by a pulsating transport mechanism operating on a subhorizontal crack linking the summit reservoir to the east rift of Kilauea. The crack acts like a buffer in which a batch of fluid (magma and/or gas) accumulates over a period of 1–3 min before being rapidly injected into a larger reservoir (possibly the east rift) over a timescale of 5–10 s. The seismic moment and volume change associated with a typical batch of fluid are approximately 1014 N m and 3000 m3, respectively. Our results also point to the existence of a single force component with amplitude of 109 N, which may be explained as the drag force generated by the flow of viscous magma through a narrow constriction in the flow path. The total volume of magma associated with the 4.5-hour-long activation of the pulsating source is roughly 500,000 m3 in good agreement with the integrated volume flow rate of magma estimated near the eruptive site.

Bubble collapse as the source of tremor at Old Faithful Geyser

Old Faithful Geyser, Yellowstone, was used as a natural laboratory for fluid-flow-induced seismic activity. Pressure measurements within the geysers water column, obtained simultaneously with seismic measurements on the surface, demonstrated that the tremor observed at Old Faithful results from impulsive events in the geyser. Tremor intensity is controlled by the rate of occurrence of these impulsive events. There is no resonance observed within the water column. The impulsive events are modeled by a collapse of a spherical bubble, including the effects of residual non-condensible gas and damping. The pressure data can be explained by a collapse of a ∼5 cm radius bubble driven by a pressure difference of ΔP = 0.3×10^5 Pa and effective viscosity ν_E = 0.04 m^2/s. Using a quasi-static geyser model, we treat the individual bubble collapses as cooling events that occur when the water column reaches a critical temperature. Their rate of occurrence is controlled by the heating rate dT/dt of the water column. As a result, the intensity of the hydrothermal and seismic activities is determined by the heat and mass input rate into the geyser. It is demonstrated that a sharp widening of the conduit can cause the number of events per unit time to drop (as observed) while the water level is still rising and heat is being input, and thus the tremor intensity can be modulated by variations in the conduit shape.

Global oceanic microseism sources as seen by seismic arrays and predicted by wave action models.

We analyze global microseism excitation patterns between July 2000 and June 2001. Seismological observations are compared with modeling results to isolate robust activity features of relevant source processes. First, we use observations of microseism source locations estimated by Landes et al. (2010) based on array processing of ambient noise correlations. Second, we construct synthetic activity patterns by coupling sea state estimates derived from wave action models to the excitation theory for microseisms. The overall spatiotemporal evolution of both estimates is characterized by a seasonal character that is associated with strong activity during winter months. The distribution of landmass causes seasonal changes on the Northern Hemisphere (NH) to exceed the variability on the Southern Hemisphere (SH). Our systematic comparison of the two estimates reveals significant microseism excitation along coastlines and in the open ocean. Since coastal reflections are not accounted for in the modeling approach, the consistent mismatch between near-coastal observations and predictions suggests that relevant microseism energy arriving at the networks is generated in these areas. Simultaneously, systematic coincidence away from coastlines verifies the open ocean generation hypothesis. These conclusions are universal and robust with respect to the seismic network locations on the NH. The spatially homogeneous resolution of our synthetics provides a valuable resource for the assessment of the global microseism weather. Similar to previously identified hot spot areas in the North Atlantic, the modeled distributions hypothesize regions of strong localized activity on the SH, which are only partially confirmed by the analyzed data sets.

Optimized Autonomous Space In-situ Sensor-Web for Volcano Monitoring

In response to NASAs announced requirement for Earth hazard monitoring sensor-web technology, a multidisciplinary team involving sensor-network experts (Washington State University), space scientists (JPL), and earth scientists (USGS cascade volcano observatory (CVO)), is developing a prototype dynamic and scaleable hazard monitoring sensor-web and applying it to volcano monitoring. The combined optimized autonomous space - in-situ sensor-web (OASIS) will have two-way communication capability between ground and space assets, use both space and ground data for optimal allocation of limited power and bandwidth resources on the ground, and use smart management of competing demands for limited space assets. It will also enable scalability and seamless infusion of future space and in-situ assets into the sensor-web. The prototype will be focused on volcano hazard monitoring at Mount St. Helens, which has been active since October 2004. The system is designed to be flexible and easily configurable for many other applications as well. The primary goals of the project are: 1) integrating complementary space (i.e., Earth observing one (EO-1) satellite) and in-situ (ground-based) elements into an interactive, autonomous sensor-web; 2) advancing sensor-web power and communication resource management technology; and 3) enabling scalability for seamless infusion of future space and in-situ assets into the sensor-web. To meet these goals, we are developing: 1) a test-bed in-situ array with smart sensor nodes capable of making autonomous data acquisition decisions; 2) efficient self-organization algorithm of sensor-web topology to support efficient data communication and command control; 3) smart bandwidth allocation algorithms in which sensor nodes autonomously determine packet priorities based on mission needs and local bandwidth information in real-time; and 4) remote network management and reprogramming tools. The space and in-situ control components of the system will be integrated such that each element is capable of autonomously tasking the other. Sensor-Web data acquisition and dissemination will be accomplished through the use of the open geospatial consortium sensor-web enablement protocols. The three-year project will demonstrate end-to-end system performance with the in-situ test-bed at Mount St. Helens and NASAs EO-1 platform.

Optimized Autonomous Space In-Situ Sensor Web for Volcano Monitoring

In response to NASAs announced requirement for Earth hazard monitoring sensor-web technology, a multidisciplinary team involving sensor-network experts (Washington State University), space scientists (JPL), and Earth scientists (USGS Cascade Volcano Observatory (CVO)), have developed a prototype of dynamic and scalable hazard monitoring sensor-web and applied it to volcano monitoring. The combined Optimized Autonomous Space - In-situ Sensor-web (OASIS) has two-way communication capability between ground and space assets, uses both space and ground data for optimal allocation of limited bandwidth resources on the ground, and uses smart management of competing demands for limited space assets. It also enables scalability and seamless infusion of future space and in-situ assets into the sensor-web. The space and in-situ control components of the system are integrated such that each element is capable of autonomously tasking the other. The ground in-situ was deployed into the craters and around the flanks of Mount St. Helens in July 2009, and linked to the command and control of the Earth Observing One (EO-1) satellite.

Statistical Approaches to Detecting Transient Signals in GPS: Results from the 2009–2011 Transient Detection Exercise

We present the results of our participation in four phases of the Southern California Earthquake Center (SCEC) transient detection exercise (Lohman and Murray, 2013). In each phase, a blind test was conducted in which sets of synthetic Global Positioning Systems (GPS) data were released and a deadline set for submission of detection results. For each data set, the presence or absence of transient events was to be determined, and the location and time of each specified. After all submissions were received, the ground‐truth information about any transient signals in the data was released. The synthetic data sets were generated by FAKENET, a software package that produces realistic GPS time series that include secular motion and seasonal signals as well as realistic noise and distributions of missing data (Agnew, 2013). Station locations in the synthetic data set were a subset of GPS installations in the western United States. In this work, we pursue a purely data‐driven approach to transient detection, rather than one based on an assumption of an underlying physical model. We view this approach as having two important advantages. First, it facilitates the detection of events, which might happen through a previously unknown, but geophysically interesting, physical process or on a previously unknown fault or structure. Second, it enables the detection of events, which have nothing to do with the solid earth but, although not the subject of the SCEC exercise, have scientific or practical merit. These include signals such as those due to atmospheric phenomena as well as signals, which result from hardware faults or failures and software processing glitches. The four phases of the exercise were conducted over approximately two years. As a result, our approach evolved as we learned from experiences in the initial phases as well as from other ongoing work during that period. The …

Modeling and On-the-Fly Solutions for Solid Earth Sciences: Web Services and Data Portal for Earthquake Early Warning System

We report on a unified on-the-fly, Web services-based observation/analysis/modeling environment for crustal deformation and natural hazards research, intended as a plug-in service for early warning systems, transfer of rapid information to civilian decision makers and the media, and educational purposes. We demonstrate an early warning system for a large earthquake in southern California using the components developed under several NASA-funded projects, including real-time GPS network infrastructure, Geophysical Resources Web Services, and GPS Explorer data portal with its on-the-fly earthquake modeling software. We generate an on-the-fly earthquake fault model based on simulated real-time (dynamic and coseismic) displacements computed by the GPS network, and viewable through GPS Explorer. Our objective is to demonstrate an operational service that could be transitioned to appropriate civilian agencies in southern California.

Geophysical Investigations of Habitability in Ice‐Covered Ocean Worlds

Geophysical measurements can reveal the structure of icy ocean worlds and cycling of volatiles. The associated density, temperature, sound speed, and electrical conductivity of such worlds thus characterizes their habitability. To explore the variability and correlation of these parameters, and to provide tools for planning and data analyses, we develop 1-D calculations of internal structure, which use available constraints on the thermodynamics of aqueous MgSO

System Architecting and System-on-Chip Design of Intelligent Sensor Networks for Active Volcanoes

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Seismic Wave Propagation in Icy Ocean Worlds

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