Phillip Dawson, IV
Phillip Dawson is a geophysicist with the U.S. Geological Survey’s Volcano Science Center, focusing on theoretical and experimental investigations of active volcanism and volcanic processes.
Phillip Dawson hails from a small town located on the flank of one of the world's largest stratovolcanoes - Mount Shasta, California. Who wouldn't want to pursue a career studying volcanoes at the USGS given that background?
He currently works as a geophysicist on the Seismology of Magmatic Injection project at the California Volcano Observatory, Moffett Field, California. This project is dedicated to understanding the underlying physics driving volcanic seismicity and processes through the use of detailed field experiments and the application, modification, and extension of existing seismic methods and theories. Objectives include: quantification of volcanic velocity structure using tomography and surface-wave dispersion inversions; inversion of broadband waveform data to quantify magma transport processes; determining the effect of tilt on modern broadband seismic sensors, and correcting for this effect using waveform inversions; quantification of the effects of 3D topography and structure on seismic wave propagation; using dense small-aperture arrays to identify source, path, and site effects in tremor wavefields; quantification of the source parameters of long-period (LP) and very-long-period (VLP) volcanic seismicity; and developing techniques to enable the accurate identification of volcanic seismicity.
Science and Products
Shallow-velocity models at the Kilauea Volcano, Hawaii, determined from array analyses of tremor wavefields
Long-period events and tremor at Popocatepetl volcano (1994–2000) and their broadband characteristics
Identifying elements of the plumbing system beneath Kilauea Volcano, Hawaii, from the source locations of very-long-period signals
Very-long-period volcanic earthquakes beneath Mammoth Mountain, California
Mapping the sources of the seismic wave field at Kilauea volcano, Hawaii, using data recorded on multiple seismic Antennas
Source mechanism of very-long-period signals accompanying dome growth activity at Merapi volcano, Indonesia
Experimental observations of pressure oscillations and flow regimes in an analogue volcanic system
Wavefield properties of a shallow long-period event and tremor at Kilauea Volcano, Hawaii
Spatial extent of a hydrothermal system at Kilauea Volcano, Hawaii, determined from array analyses of shallow long-period seismicity 1. Method
Spatial extent of a hydrothermal system at Kilauea Volcano, Hawaii, determined from array analyses of shallow long-period seismicity 2. Results
Temporal and spectral characteristics of seismicity observed at Popocatepetl volcano, central Mexico
Broadband measurements of the sources of explosions at Stromboli Volcano, Italy
Science and Products
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Filter Total Items: 28
Shallow-velocity models at the Kilauea Volcano, Hawaii, determined from array analyses of tremor wavefields
The properties of the surface wavefield at Kilauea Volcano are analysed using data from small-aperture arrays of short-period seismometers deployed in and around the Kilauea caldera. Tremor recordings were obtained during two Japan-US cooperative experiments conducted in 1996 and 1997. The seismometers were deployed in three semi-circular arrays with apertures of 300, 300 and 400 m, and a linear aAuthorsG. Saccorotti, B. Chouet, P. DawsonLong-period events and tremor at Popocatepetl volcano (1994–2000) and their broadband characteristics
Following an initial phreatic eruption on 21 December 1994, activity at Popocatepetl has been dominated by fumarolic emissions interspersed with more energetic emissions of ashes and gases. A phase of repetitive dome-building and dome-destroying episodes began in March 1996 and is still ongoing at present. We describe the long-period (LP) seismicity accompanying eruptive activity at Popocatepetl fAuthorsA. Arciniega-Ceballos, B. Chouet, P. DawsonIdentifying elements of the plumbing system beneath Kilauea Volcano, Hawaii, from the source locations of very-long-period signals
We analyzed 16 seismic events recorded by the Hawaiian broad-band seismic network at Kilauca Volcano during the period September 9-26, 1999. Two distinct types of event are identified based on their spectral content, very-long-period (VLP) waveform, amplitude decay pattern and particle motion. We locate the VLP signals with a method based on analyses of semblance and particle motion. Different souAuthorsJ. Almendros, B. Chouet, P. Dawson, T. BondVery-long-period volcanic earthquakes beneath Mammoth Mountain, California
Detection of three very‐long‐period (VLP) volcanic earthquakes beneath Mammoth Mountain emphasizes that magmatic processes continue to be active beneath this young, eastern California volcano. These VLP earthquakes, which occurred in October 1996 and July and August 2000, appear as bell‐shaped pulses with durations of one to two minutes on a nearby borehole dilatometer and on the displacement seisAuthorsDavid P. Hill, P. Dawson, M.J.S. Johnston, A. M. Pitt, G. Biasi, K. SmithMapping the sources of the seismic wave field at Kilauea volcano, Hawaii, using data recorded on multiple seismic Antennas
Seismic antennas constitute a powerful tool for the analysis of complex wave fields. Well-designed antennas can identify and separate components of a complex wave field based on their distinct propagation properties. The combination of several antennas provides the basis for a more complete understanding of volcanic wave fields, including an estimate of the location of each individual wave-field cAuthorsJ. Almendros, B. Chouet, P. Dawson, Caleb G. HuberSource mechanism of very-long-period signals accompanying dome growth activity at Merapi volcano, Indonesia
Very-long-period (VLP) pulses with period of 6–7s, displaying similar waveforms, were identified in 1998 from broadband seismographs around the summit crater. These pulses accompanied most of multiphase (MP) earthquakes, a type of long-period event locally defined at Merapi Volcano. Source mechanisms for several VLP pulses were examined by applying moment tensor inversion to the waveform data. SolAuthorsD. Hidayat, B. Chouet, B. Voight, P. Dawson, Antonius RatdomopurboExperimental observations of pressure oscillations and flow regimes in an analogue volcanic system
Gas-liquid flows, designed to be analogous to those in volcanic conduits, are generated in the laboratory using organic gas-gum rosin mixtures expanding in a vertically mounted tube. The expanding fluid shows a range of both flow and pressure oscillation behaviors. Weakly supersaturated source liquids produce a low Reynolds number flow with foam expanding from the top surface of a liquid that exhiAuthorsS.J. Lane, B. A. Chouet, J.C. Phillips, P. Dawson, G.A. Ryan, E. HurstWavefield properties of a shallow long-period event and tremor at Kilauea Volcano, Hawaii
The wavefields of tremor and a long-period (LP) event associated with the ongoing eruptive activity at Kilauea Volcano, Hawaii, are investigated using a combination of dense small-aperture (300 m) and sparse large-aperture (5 km) arrays deployed in the vicinity of the summit caldera. Measurements of azimuth and slowness for tremor recorded on the small-aperture array indicate a bimodal nature of tAuthorsG. Saccorotti, B. Chouet, P. DawsonSpatial extent of a hydrothermal system at Kilauea Volcano, Hawaii, determined from array analyses of shallow long-period seismicity 1. Method
We present a probabilistic method to locate the source of seismic events using seismic antennas. The method is based on a comparison of the event azimuths and slownesses derived from frequency-slowness analyses of array data, with a slowness vector model. Several slowness vector models are considered including both homogeneous and horizontally layered half-spaces and also a more complex medium repAuthorsJ. Almendros, B. Chouet, P. DawsonSpatial extent of a hydrothermal system at Kilauea Volcano, Hawaii, determined from array analyses of shallow long-period seismicity 2. Results
Array data from a seismic experiment carried out at Kilauea Volcano, Hawaii, in February 1997, are analyzed by the frequency-slowness method. The slowness vectors are determined at each of three small-aperture seismic antennas for the first arrivals of 1129 long-period (LP) events and 147 samples of volcanic tremor. The source locations are determined by using a probabilistic method which comparesAuthorsJ. Almendros, B. Chouet, P. DawsonTemporal and spectral characteristics of seismicity observed at Popocatepetl volcano, central Mexico
Popocatepetl volcano entered an eruptive phase from December 21, 1994 to March 30, 1995, which was characterized by ash and fumarolic emissions. During this eruptive episode, the observed seismicity consisted of volcano-tectonic (VT) events, long-period (LP) events and sustained tremor. Before the initial eruption on December 21, VT seismicity exhibited no increase in number until a swarm of VT eaAuthorsA. Arciniega-Ceballos, C. Valdes-Gonzalez, P. DawsonBroadband measurements of the sources of explosions at Stromboli Volcano, Italy
During September–October 1997, 21 three-component broadband seismometers were deployed on Stromboli Volcano at radial distances of 0.3–2.2 km from the active crater to investigate the source mechanisms of Strombolian explosions. In the 2–50 s band, the very-long period (VLP) signals associated with explosions are consistent with two stationary sources repeatedly activated in time. VLP particle motAuthorsB. Chouet, G. Saccorotti, P. Dawson, M. Martini, R. Scarpa, G. De Luca, G. Milana, M. Cattaneo