Data collected from the various observatories were used to create different types of data products. Each data product addressed a different scientific problem.
P-Wave Tomography Tomography is a method of producing a three-dimensional image of the internal structures of a solid object (such as the human body or the earth) by the observation and recording of differences in the effects on the passage of energy waves impinging on those structures. The waves of energy are P-waves generated by earthquakes and are recording the wave velocities. The high quality data that was collected by the permanent seismic stations of USArray and the Advanced National Seismic System (ANSS) allowed the creation of high resolution seismic imaging of the Earth's interior below the United States. Seismic tomography helps constrain mantle velocity structure and aids in the understanding of chemical and geodynamic processes that are at work. With the use of the data collected by USArray and global travel-time data, a global tomography model of P-wave velocity heterogeneity in the mantle could be created. The range and resolution of this technique allowed investigation into the suite of problems that are of concern in the North American mantle lithosphere, including the nature of the major tectonic features. This method gives evidence for differences in thickness and the velocity anomaly of the
mantle lithosphere between the stable center of the continent and the more active western North America. These data are vital for the understanding of local lithosphere evolution, and when combined with additional global data, allow the mantle to be imaged beyond the current extent of USArray.
Receiver Reference Models EarthScope Automated Receiver Survey (EARS), created a prototype of a system that was used to address several key elements of the production of EarthScope products. One of the prototype systems was the receiver reference model. It provided crustal thickness and average crustal Vp/Vs ratios beneath USArray transportable array stations.
Ambient Seismic Noise The main function of the Advanced National Seismic System (ANSS) and USArray, was to provide high quality data for earthquake monitoring, source studies and Earth structure research. The utility of seismic data is greatly increased when noise levels, unwanted vibrations, are reduced; however broadband seismograms will always contain a certain level of noise. The dominant sources of noise are either from the instrumentation itself or from ambient Earth vibrations. Normally, seismometer self noise will be well below the seismic noise level, and every station will have a characteristic noise pattern that can be calculated or observed. Sources of
seismic noise within the Earth are caused by any of the following: the actions of human beings at or near the surface of the Earth, objects moved by wind with the movement being transferred to the ground, running water (river flow), surf, volcanic activity, or long period tilt due to thermal instabilities from poor station design. A new approach to seismic noise studies was introduced with the EarthScope project, in that there were no attempts to screen the continuous waveforms to eliminate body and
surface waves from the naturally occurring earthquakes. Earthquake signals are not generally included in the processing of noise data, because they are generally low probability occurrences, even at low power levels. The two objectives behind the collection of the seismic noise data were to provide and document a standard method to calculate ambient seismic background noise, and to characterize the variation of ambient background seismic noise levels across the United States as a function of
geography, season, and time of day. The new statistical approach provided the ability to compute probability density functions (PDFs) to evaluate the full range of noise at a given seismic station, allowing the estimation of noise levels over a broad range of frequencies from 0.01–16 Hz (100-0.0625s period). With the use of this new method it became much easier to compare seismic noise characteristics between different networks in different regions.
Earthquake Ground Motion Animations Seismometers of USArray transportable array recorded the passage of numerous seismic waves through a given point near the Earth's surface, and classically these seismograms are analyzed to deduce properties of the Earth's structure and the seismic source. Given a spatially dense set of seismic recordings, these signals could also be used to visualize the actual continuous seismic waves, providing new insights and interpretation techniques into complex wave propagation effects. Using signals recorded by the array of seismometers, the EarthScope project animated seismic waves as they sweep across the USArray transportable array for selected larger earthquakes. This illustrated the regional and teleseismic wave propagation phenomena. The seismic data collected from both permanent and transportable seismic stations was used to provide these computer generated animations.
Regional Moment Tensors The seismic moment tensor is one of the fundamental parameters of earthquakes that can be determined from seismic observations. It is directly related to earthquake fault orientation and rupture direction. The
moment magnitude, Mw derived from the moment tensor magnitude, is the most reliable quantity for comparing and measuring the size of an earthquake with other earthquake magnitudes. Moment tensors are used in a wide range of seismological research fields, such as earthquake statistics, earthquake scaling relationships, and stress inversion. The creation of regional moment tensor solutions, with the appropriate software, for moderate-to-large earthquakes in the U.S. came from USArray transportable array and Advance National Seismic System broadband seismic stations. Results were obtained in the time and the frequency domain. Waveform fit and amplitude-phase match figures were provided to allow users to evaluate moment tensor quality.
Geodetic Monitoring of the Western US and Hawaii Global Positioning System (GPS) equipment and techniques provide a unique opportunity for earth scientists to study regional and local tectonic plate motions and conduct natural hazards monitoring. Cleaned network solutions from several GPS arrays merged into regional clusters in conjunction with the EarthScope project. The arrays included the Pacific Northwest Geodetic Array, EarthScope's Plate Boundary Observatory, the Western Canadian Deformation Array, and networks run by the US Geological Survey. The daily GPS measurements from ~1500 stations along the Pacific/North American
plate boundary provided millimeter-scale accuracy and could be used monitor the displacements of the earths crust. With the use of data modeling software and the recorded GPS data, the opportunity to quantify crustal deformation caused by
plate tectonics, earthquakes,
landslides and volcanic eruptions was possible.
Time-dependent Strain The goal was to provide models of time-dependent strain associated with a number of recent earthquakes and other geologic events as constrained by GPS data. With the use of
InSAR (Interferometric Synthetic Aperture Radar), a remote-sensing technique, and PBO (Plate Boundary Observatory), a fixed array of GPS receivers and strainmeters, the EarthScope project provided spatially continuous strain measurements over wide geographic areas with decimeter to centimeter resolution.
Global Strain Rate Map The Global Strain Rate Map (GSRM) is a project of the International Lithosphere Program whose mission is to determine a globally self-consistent strain rate and velocity field model, consistent with geodetic and geologic field observations collected by GPS, seismometers, and strainometers. GSRM is a digital model of the global velocity gradient tensor field associated with the accommodation of present-day crustal motions. The overall mission also includes: (1) contributions of global, regional, and local models by individual researchers; (2) archive existing data sets of geologic, geodetic, and seismic information that can contribute toward a greater understanding of strain phenomena; and (3) archive existing methods for modeling strain rates and strain transients. A completed global strain rate map provided a large amount of information which will contribute to the understanding of continental dynamics and for the quantification of seismic hazards. == Science ==