Bob Smalley

• University of Memphis

From cadastre and engineering to scientific uses, many practical applications of Geodetic Reference Frames (GRFs) require site coordinates in a reference or conventional epoch (CE) that is different from the observation epoch. Because the Earth is dynamic and coordinates in a GRF are not static, when combining georeferenced features measured at dif...

GNSS trajectory prediction modeling is necessary to obtain the time evolution of arbitrary points located between GNSS stations in a geodetic reference frame. If the GNSS-defined reference frame includes areas that experience coseismic deformation, its trajectory model needs to incorporate an estimate of the static deformation field generated by se...

On August 21, 2017 a total solar eclipse crossed the United States from the Pacific to Atlantic coasts. For the first time during this event, an ionospheric total electron content (TEC) bow wave produced by the shadow of the moon, theorized in the early 1970s, was recorded by thousands of GNSS stations in North America. Several authors analyzed the...

A quick rebound for Antarctic crust Earth's crust deforms under the load of glaciers and ice sheets. When these masses are removed, the crust rebounds at a time scale determined by the viscosity of the upper mantle. Using GPS, Barletta et al. found that the viscosity of the mantle under the West Antarctic Ice Sheet is much lower than expected. This...

Since its creation in 1998, the Argentine Continuous Satellite Monitoring Network (Red Argentina de Monitoreo Satelital Continuo [RAMSAC]) has grown to include more than 100 continuously operating Global Navigation Satellite Systems (GNSS) stations in Argentina. RAMSAC Receiver Independent Exchange Format (RINEX) data and their derived positioning...

We calculated surface displacements produced by a synthetic megathrust earthquake using two spherical, layered, elastic dislocation models which differ only in that one model accounts for the coupling between elasticity and gravity and the other does not. We show that including gravity perturbs the displacement field differently in the near-, mediu...

A new GPS-derived surface velocity field for the central Andean backarc permits an assessment of orogenic wedge deformation across the southern Subandes of Bolivia, where recent studies suggest that great earthquakes (>Mw 8) are possible. We find that the backarc is not isolated from the main plate boundary seismic cycle. Rather, signals from subdu...

We demonstrate a flexible strategy for local tsunami warning that relies on regional geodetic and seismic stations. Through retrospective analysis of four recent tsunamigenic events in Japan and Chile, we show that rapid earthquake source information, provided by methodologies developed for earthquake early warning, can be used to generate timely e...

The 2010, (Mw 8.8) Maule, Chile, earthquake produced large co-seismic displacements and non-secular, post-seismic deformation, within latitudes 28(Formula presented.)S–40(Formula presented.)S extending from the Pacific to the Atlantic oceans. Although these effects are easily resolvable by fitting geodetic extended trajectory models (ETM) to contin...

Least squares collocation (LSC) has been successfully applied to develop the Velocity Model for SIRGAS (VEMOS) (Drewes and Heidbach, 2012) used to predict the velocities in the Geocentric Reference System for the Americas (Sistema de Referencia Geocéntrico para las Américas, SIRGAS) GNSS reference frame. After the 2010 (Mw 8.8) Maule, Chile earthqu...

We identified co-seismic ionospheric disturbances (CID) in Antarctica generated by the 2010 Maule and the 2011 Tohoku-Oki earthquakes analyzing TEC data with a modified beamforming technique. Beamforming in Antarctica, however, is not straightforward due to the effects of array deformation and atmospheric neutral wave-ionospheric plasma coupling. W...

Global Navigation Satellite System data across the New Madrid seismic zone (NMSZ) in the central United States over the period from 2000 through 2014 are analyzed and modeled with several deformation mechanisms including: (1) creep on subsurface dislocations; (2) postseismic frictional afterslip and viscoelastic relaxation from the 1811–1812 and 14...

Several recent great earthquakes have produced regional to continental sized non-secular post-seismic deformation fields that are easily resolvable with GPS, requiring further development of geodetic reference frame velocities to include these effects. The 2010, (Mw 8.8) Maule, Chile, earthquake produced a measurable, non-secular, post-seismic sign...

The traditional approach to both earthquake and Global Positioning System (GPS) location problems in a homogeneous half‐space produces a nonlinear relationship between a set of known positions, seismic stations or GPS satellites, and an unknown point, an earthquake hypocenter or GPS receiver. Linearization, followed by an iterative inversion, is ty...

El método de colocación por mínimos cuadrados (Moritz, 1978) ha sido aplicado con éxito para el desarrollo del modelo de velocidades VEMOS (Drewes y Heidbach, 2012) para predecir las velocidades del marco de referencia GNSS SIRGAS. Luego del sismo de Maule (Mw 8.8), Chile en 2010, la deformación co- y post-sísmica ha modificado tanto la velocidad c...

The South Scotia Ridge Transform (SSRT) plate boundary between the Scotia and Antarctic plates experienced large strike-slip earthquakes on August 4, 2003 (Mw 7.6) and November 17, 2013 (Mw 7.8). These events have overlapping aftershock zones, which is unusual. A 36°–45° southward dipping fault zone ruptured with left-lateral displacements in each...

GPS total electron content (TEC) measurements are commonly used to study ionospheric disturbances in the near and far field. For co-seismic ionospheric disturbances (CIDs) the apparent velocity of the signal can be calculated from distance travel-time plots or interferometric stacking techniques. To date, signals related to solid earth-atmosphere c...

The traditional approach to both earthquake and GPS location problems in a homogeneous half-space produces a nonlinear relationship between a set of known positions, seismic stations or GPS satellites, and an unknown point, an earthquake hypocenter or GPS receiver. Lineariza-tion, followed by an iterative inversion, is typically used to solve both...

[1] Observations of coseismic and postseismic deformation associated with the 2010 Mw = 8.8 Maule earthquake in south-central Chile provide constraints on the spatial heterogeneities of frictional properties on a major subduction megathrust and how they have influenced the seismic rupture and postseismic effects. We find that the bulk of coseismic...

Abstract The surface of the Earth deforms in response to changes in the loads imposed upon it by the atmosphere the cryosphere and the hydrosphere. Of particular interest is the load exerted on the Earth by ice and water masses present on its surface. Global Positioning System (GPS) instruments can measure the deformation signal of the Earth. We me...

The Maule earthquake of 27th February 2010 (Mw = 8.8) affected ~ 500 km of the Nazca-South America plate boundary in south-central Chile producing spectacular crustal deformation. Here, we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous GPS, both in near- and far-field regions. Earthquake slip al...

Position time series from Global Positioning System (GPS) stations in the New Madrid region were differenced to determine the relative motions between stations. Uncertainties in rates were estimated using a three-component noise model consisting of white, flicker, and random walk noise, following the methodology of Langbein, 2004. Significant motio...

The Antarctica component of the NSF supported POLENET GPS network is an autonomous, continuously recording GPS network that sends GPS phase data files on a daily basis via satellite to the UNAVCO Facility (UF) Archive. The data are openly available from the UF Archive upon receipt. We have developed a system for automatically processing the continu...

We report on the results of both campaign and continuous GPS measurements performed over the past 17 years in the area of the Southern and Northern Patagonian Ice Fields of Chile and Argentina. The network is composed of ~60 campaign sites and ~10 continuous sites that provide a relatively dense, 2-D sampling of the deformation field associated wit...

The surface of the Earth deforms in response to changes in the loads imposed upon it by the atmosphere the cryosphere and the hydrosphere. Of particular interest is the load exerted on the Earth by ice and water masses present on its surface. Global Positioning System (GPS) instruments can measure the deformation signal of the Earth. We measured th...

Of the 3 great earthquakes to have occurred in the GPS observational era, the proximity to Andes of the 2010 Maule event offers the most promise in relating subduction-zone forcing to active orogenic process. In particular, the backarc in this part of the Andes is unique because Quaternary fold and thrust belt shortening rates are almost negligible...

Abstract Available from http://www.agu.org

Large earthquakes produce crustal deformation that can be quantified by geodetic measurements, allowing for the determination of the slip distribution on the fault. We used data from Global Positioning System (GPS) networks in Central Chile to infer the static deformation and the kinematics of the 2010 moment magnitude (M(w)) 8.8 Maule megathrust e...

Static offsets produced by the February 27, 2010 Mw = 8.8 Maule, Chile earthquake as measured by GPS and InSAR constrain coseismic slip along a section of the Andean megathrust of dimensions 650 km (in length) x 180 km (in width). GPS data have been collected from both campaign and continuous sites sampling both the near-field and far field. ALOS/P...

The Mw=8.8 Chile earthquake of February 27, 2010, provided an excellent opportunity for high-rate GPS seismology within and around its epicentral region. We used TRACK to estimate strong motion displacement time series from 1Hz data at a 5 station array of HRGPS stations in Tucumán, Argentina, ~1130 km from the epicenter. These HRGPS stations, with...

Because the signal is so big, great earthquakes allow us to make quantum leaps in our understanding of Earth deformation process and material properties. The Maule earthquake, with its occurrence near a large subaerial landmass and the large numbers of instruments available to study it, will surely become one of the most important geophysical event...

The amount of continuous GPS (cGPS) stations deployed in southern South America (0°-54°S) was largely increased over the decade before the 27 February 2010 Maule earthquake to reach a total of 25 stations. 43 new cGPS have been installed after such event, near and around the ruptured area. This is by far the best geodetically-observed megathrust ea...

Radar interferometry from the ALOS satellite captured the coseismic ground deformation associated with the 2010 Mw 8.8 Maule, Chile earthquake. We processed the ALOS interferograms with our newly developed GMTSAR software. The ScanSAR to stripe mode and the ScanSAR to ScanSAR interferograms along the descending orbits are critical to recover a near...

The February 27, 2010 Mw 8.8 earthquake struck southern Chile on the primary fault that defines the interface where the Nazca Plate subducts below the South American continent. The earthquake ruptured an area approximately 400 km in the along strike direction and about 200 km in the down dip direction. The availability of extensive geodetic data fr...

Lateral crustal velocity variations across the Andean Foreland in San Juan Argentina are explored by joint hypocentral determination (JHD) analysis and 3D velocity inversion. JHD results show consistent positive station corrections beneath Precordillera and negative station corrections beneath Pie de Palo, corresponding to regions of low and high v...

The southern Andes associated with the 2010 and 1960 megathrust earthquakes are characterized by a narrow cordillera, relatively low elevations ( 4000 m), large amounts of Neogene crustal shortening, and andesitic-dacitic stratovolcanoes and ignimbrite complexes that are restricted to the arc. Furthermore, in contrast to the currently active fold a...

Synoptic observational data are being provided by new arrays of GNSS and seismic sensors distributed across West Antarctica from the Antarctic Network (A-NET) component of the IPY Polar Earth Observing Network (POLENET). Providing this invaluable new trove of data to the global science community and the major increase in observational capacity are...

Radar interferometry from the ALOS satellite captured the coseismic ground deformation associated with the 2010 Mw 8.8 Maule, Chile earthquake. The ALOS interferograms reveal a sharp transition in fringe pattern at ~150 km from the trench axis that is diagnostic of the downdip rupture limit of the Maule earthquake. An elastic dislocation model base...

The 27 February 2010 (M 8.8) Maule, Chile Earthquake, the fifth largest earthquake ever recorded, occurred in south-central Chile, abutting and only slightly overlapping the rupture area of the 1960 (M 9.5) Valdivia Earthquake, the largest earthquake ever recorded. The 2010 megathrust occurred in an area which has been studied by several geodesy gr...

In the context of critical taper wedge mechanics, we analyze a new GPS-derived surface velocity field from the southern Subandean (SSA) range on the east flank of the central Andean Plateau. The SSA is one of the few active orogenic wedges located far enough from a plate boundary so that the geodetic signature of contractional processes may be isol...

1] We use seismic array processing of high-rate GPS (HRGPS) displacement time series from the Great, 2004, M w 9+, Sumatra-Andaman earthquake recorded at over 90 nonuniformly distributed HRGPS stations in central North America to determine the fundamental Love wave phase velocity dispersion curve there. These measurements were performed using frequ...

We present preliminary geodetic estimates for vertical bedrock velocity at twelve survey GPS stations in the West Antarctic GPS Network, an additional survey station in the northern Antarctic Peninsula, and eleven continuous GPS stations distributed across the continent. The spatial pattern of these velocities is not consistent with any postglacial...

We present the initial results of the West Antarctic GPS Network (WAGN), which was initiated in the 2002/03 Antarctic field season. Specifically we present vertical velocity estimates for all WAGN stations with a total occupational time span of 3 years or more. Most of these station have been observed for at least four years, and many for 5 years o...

The Polar Earth Observing Network (POLENET) multinational consortium has begun deployment of new networks of in situ sensors in the Arctic and across Antarctica for the International Polar Year (IPY). The West Antarctic component of POLENET, led by U.S. investigators, will consist of 16 co-located continuous GPS stations and broadband seismic senso...

The December 2004 Sumatra-Andaman earthquake was the second largest (Mw 9.3) and second deadliest (280,000 casualties) earthquake ever recorded. It was also unusual in that it combined a normal 'fast' rupture with a more unusual slow fault slip event. This unique occurrence presents an important opportunity to examine two questions with potentially...

We have implemented the Earthquake Locator Interactive Demonstration (ELID) as an addition to introductory earthquake lab exercises for the purpose of helping students build their intuitive knowledge of earthquake properties. The earthquake lab exercises used for this project originally incorporated the common circle method to locate an earthquake'...

One of the most contentious issues related to earthquake hazards in the United States centers on the midcontinent and the origin, magnitudes, and likely recurrence intervals of the 1811-1812 New Madrid earthquakes that occurred there. The stakeholder groups in the debate (local and state governments, reinsurance companies, American businesses, and...

New GPS measurements demonstrate tectonic segmentation of the South Shetland Islands platform, regarded as a microplate separating the Antarctic Peninsula from the oceanic portion of the Antarctic plate. King George, Greenwich, and Livingston islands on the central and largest segment are separating from the Antarctic Peninsula at 7–9 mm/a, moving...

Temporary deformation in great earthquake cycles and permanent shear deformation associated with oblique plate convergence both provide critical clues for understanding geodynamics and earthquake hazard at subduction zones. In the region affected by the Mw 9.5 great Chile earthquake of 1960, we have obtained GPS observations that provide informatio...

We have implemented the Earthquake Locator Interactive Demonstration (ELID) as an addition to introductory earthquake lab exercises for the purpose of helping students build their intuitive knowledge of earthquake properties. The earthquake lab exercises used for this project originally incorporated the common circle method to locate an earthquake'...

Continued study of the New Madrid seismic zone further deepens the enigma of the world's&p most active intraplate seismic zone. Paleoseismic studies indicate the occurrence, with an approximate 500 year recurrence interval, of three to four previous events or sequences of several clustered events. Newer estimations of the magnitudes of the events i...

We obtain the first Scotia and South Sandwich plate Euler vector estimates not dependent on closure using a combination of GPS crustal velocity data from the Scotia and South Sandwich plates, transform azimuths, spreading data, and an updated earthquake slip vector catalog. Neither the GPS data, which are tied to the global plate reference frame bu...

Two years after the Great Sumatra-Andaman earthquake the 3.1 m WSW coseismic displacement at Port Blair, An-daman Islands, had increased by 32 cm. Postseismic up-lift initially exceeded 1 cm per week and decreased to <1 mm/week. By 2007 points near Port Blair had risen more than 20 cm, a 24% reversal of coseismic subsidence. Up-lift at eight GPS si...

We analyze continuous and survey GPS and InSAR data from the south-central Andean thrust front in Mendoza, Argentina and focus on the Barrancas anticline, a blind thrust-related fold with evidence for Quaternary folding. In 2001 we installed a 43 station network in a ~50 km radius centered on the anticline in response to our regional analysis which...

On 26 December 2004 the Andaman Islands near Port Blair, on the hanging wall of the Sumatra/Andaman mega thrust, sank 86 cm and shifted 3.1 m WSW. Port Blair since then has continued to move WSW at an exponentially decaying rate that by mid 2006 had attained 25 cm (i.e. 8% of coseismic slip). In contrast the harbour rose 15 cm, an 18% reversal in c...

We present GPS measurements of the crustal velocity field in the southern Central Andes between the Santa Cruz corner and the Malargüe fold and thrust belt, and model this interseismic velocity field as the combination of an ephemeral, elastic signal associated with locking of the main plate boundary, and a steady and non-reversing component of dis...

When one hears that an earthquake has occurred, one of the first questions is: where was it? For the general public, this question oftentimes determines the importance of another question: how big was it? Once learning the location and size, some might wonder how this information was obtained. We present here an interactive, three-dimensional analo...

The independent analyses of GAMA (global positioning system (GPS) array in mid-America) data by Calais et al.1 demonstrate the difficulties in determining patterns of rational deformation within otherwise rigid plates. We are a long way from incorporating this type of information into seismic-hazard analysis, and we agree that longer time spans and...

The December 26, 2004 Sumatra-Andaman earthquake generated horizontal displacements at Port Blair totaling 3.08 m and vertical subsidence of 0.6-0.9m, indicating 1.6 m arc normal and 6.2±0.6 m dextral coseismic slip on the plate interface. Displacements occurred steadily beginning 10 minutes after the mainshock and were largely complete within 30 m...

Global positioning system (GPS) data from the central Andes record vertical axis rotations that are consistently counterclockwise in Peru and Bolivia north of the bend in the mountain belt, and clockwise to the south in southern Bolivia, Argentina, and Chile. These geologically instantaneous rotations have the same sense as rotations that have accr...

1] A GPS station in Manaus, near the center of the Amazon basin, manifests an annual cycle of vertical displacement with a peak-to-peak amplitude of 50– 75 mm. This is by far the largest crustal oscillation observed to date, and nearly 2 – 3 times larger than the amplitude predicted for this region. Vertical ground displacement is strongly anti-cor...

In the winter of 1811-1812, near the town of New Madrid in the central United States and more than 2,000 km from the nearest plate boundary, three earthquakes within three months shook the entire eastern half of the country and liquefied the ground over distances far greater than any historic earthquake in North America. The origin and modern signi...

We present GPS velocity solutions for the entire latitudinal range of the rupture zone of the great (Mw ~ 9.5) 1960 earthquake. Previous studies presented velocity solutions only for the northern half of this zone. The new measurements indicate that the pattern of opposing, roughly arc-normal, motions previously documented in the north also occur i...

A geodetic station (ANTC) built in bedrock in southern Chile is undergoing non-steady vertical motion within a range of nearly 50 mm. These fluctuations are dominated by the earth's local elastic response to the changing weight of water in a reservoir located about 20 km away. There is also an annual periodic component of motion that is attributed...

1] A new Global Positioning System (GPS)-derived velocity field for the Andes mountains (26°–36°S) allows analysis of instantaneous partitioning between elastic and anelastic deformation at the orogen's opposing sides. Adding an ''Andes'' microplate to the traditional description of Nazca-South America plate convergence provides the kinematic frame...

1] Global Positioning System (GPS) measurements provide the first direct measurement of plate motion and crustal deformation across the Scotia-South America transform plate boundary in Tierra del Fuego. This plate boundary accommodates a part of the overall motion between South America and Antarctica. The subaerial section of the plate boundary in...

We present velocities relative to the South American plate for five GPS stations on the Nazca plate and use these measurements to estimate the modern Euler vector. We find a pole at 55.8°N, 92.5°W with a rotation rate of 0.60 °/Myr. Because the GPS station at Easter Island appears to be moving at approximately 6.6 mm/yr relative to the other Nazca...

A key question for the cause of the New Madrid earthquakes is "what is driving the earthquakes?" In order to address this question, several ongoing GPS based geodetic projects are being performed in the New Madrid seismic zone. Initial results from campaign style GPS networks in the New Madrid area reported deformation rates suggestive of plate bou...

We present the GPS-derived velocity field from the south-central Andes mountains between 28 o and 36 oS. The GPS network covers the entire orogenic system from forearc to backarc and is especially dense over the active Precordillera fold and thrust belt in west-central Argentina. The study area coincides with the transition from flat to steeply dip...

We use Global Positioning System measurements to determine relative plate movements and crustal deformation across the Scotia - South America plate boundary. Our results clearly show active crustal deformation along the South America - Scotia transform boundary in eastern Tierra del Fuego. The 160 km subaerial section of the plate boundary there, t...

[1] Abstract: We interpret the interseismic crustal velocity field of the central Andes using a simple three-plate model in which the Andean mountain belt is treated as a rigid microplate located between the Nazca and South American (SoAm) plates. We assume that the Euler vectors associated with these plates are strictly coaxial and that the surfac...

We present an integrated velocity field for the central Andes, derived from GPS observations collected between January 1993 and March 2001 that eliminates the velocity bias between the South America-Nazca Plate Project (SNAPP) and central Andes GPS Project (CAP) velocity fields published by Norabuena et al. [1998] and Bevis et al. [1999]. The refer...

We present a preliminary analysis of aftershocks of the Mw=7.7 Republic Day (26 January) 2001 earthquake in Gujarat, India, recorded on a network of portable digital event recorders (the MAEC/ISTAR network). During the 18 day deployment, this network recorded ground motion from nearly 2000 earthquakes; almost exclusively M<5 events within about 100...

An intercomparison of recent velocity solutions for the Global Positioning System (GPS) networks constructed by the South American-Nazca Plate Project (SNAPP), based in Bolivia and Peru, and our Central Andes GPS Project (CAP), based in Chile and Argentina, indicates a velocity discontinuity of order 10 mm/yr near the boundary between these network...

High precision Global Positioning System (GPS) geodesy has emerged as a powerful new tool for the Earth sciences. Over the last decade it has revolutionized global and regional geodesy and research into crustal motion and deformation, and it shows great promise in other areas such as remote sensing of atmospheric water vapor and the ionosphere. Inc...

Local network three-component digital data from the San Juan area, Argentina, provide the first seismological images of the deep crustal structure in the Andean foreland above a horizontal segment of the subducted Nazca plate. We have identified S-to-P seismic phases converted on the Moho by analysis of seismograms formed by taking the product of t...

Data from a digitally recording seismic network in San Juan, Argentina, provide the fnst images of crustal scale basement faults beneath the Precordillera. This seismicity is near the boundary between the Precordillera (a thin-skinned thrust belt) and the Sierras Pampeanas (a region of thick-skinned basement deformation), two seismically active tec...

A digitally recording seismic network was operated from September 1987 to May 1988 in the San Juan Province of northwestern Argentina. The data provide a detailed view of the crustal seismicity of Sierra Pie de Palo, one of the most seismically active mountain blocks of the Sierra Pampeanas and the site of the destructive Ms 7.3 Caucete earthquake...

A portable array for numerical data acquisition (PANDA) was designed and built in-house at the Center for Earthquake Research and Information (CERI), Memphis State University. The features of the system are described. -after Authors

Lateral velocity variations in the Andean foreland near San Juan Province, Argentina, were detected by analyzing the station corrections computed as part of the joint location of local earthquake data. The events, recorded by a portable network (PANDA), have intermediate and shallow depths (about 100 km and less than 40 kin, respectively). The JHD...

Local network data from San Juan, Argentina, provides new information about crustal seismicity in the Andean foreland above a horizontal segment of the subducted Nazca Plate. Two areas of foreland seismicity are found, one associated with the Sierras Pampeanas basement uplifts, and the other beneath, but not within, the Precordillera foreland fold-...

Seismic data, recorded by INPRES telemetered network located above one of the subhorizontal segments of the subducted Nazca plate Wadati-Benioff zone beneath western Argentina, were analyzed to determine the zone's fine structure. The depth of the center and the thickness of the subhorizontal Wadati-Benioff zone beneath the network were calculated...

Preliminary results from the first determination of crustal velocities in the area of the New Madrid seismic zone based on two years of continuous GPS geodetic measurements indicate that velocities with respect to stable North America are small (less than 3mm/yr) and not significantly different than zero. Our results are significantly stronger than...

The Altiplano-Puna of the central Andes -- 1500 km long, 250 km wide, and 4000 m high -- is one of the great continental plateaus of the world. The SE margin of the Puna over lies the shoaling of the subducted Nazca Plate and, because of its dynamic morphology and its superb exposures, illustrates the relations between structural shortening and pla...

We present a fast, two-step method for preliminary earthquake location using the direct arrivals recorded by a local network by assuming that travel times follow a hyperbolic relationship. For a layered medium, hypocentral coordinates (xe, ye, h), arrival times (t), origin time (To), travel times of either P or S waves 0"), and station coordinates...