Geodetic Science Snapshots - Solid Earth

GNSS observations show surface horizontal displacements of 4 to 8 millimeters wobbling back and forth for more than five months and over thousands of kilometers before massive subduction zone earthquakes in Japan and Chile. Detailed modeling of the dense geodetic data for the Japan earthquake suggests a fluid-triggered slab pull helping to initiate a massive event.

A stable Caribbean reference frame 2018 (CARIB18) is developed for the Caribbean plate using long-term observations from 18 GPS stations along the margins of the plate. The results provide seven parameters for transforming positional time series from a global reference frame (IGS14) to a regional reference frame. CARIB18 is fundamental to study plate motions and other earth processes.

Extensive geologic and geodetic data, especially terrestrial LiDAR and GPS, help decipher the dynamics of the eastern Basin and Range in the Sevier Desert, Utah. Over the past 30,000 years, the extension rates on faults near the Basin and Range-Colorado Plateau Transition Zone are much higher than in the Basin and Range. In the Sevier Desert, these high rates are due to periods of volcanism that caused magma-assisted rifting to activate these faults.

High-rate GPS observations over long time periods after an earthquake were compiled to resolve weaker ground motions from large events. Analysis of long duration GPS signals for the 2011 Tohoku-Oki earthquake from the Plate Boundary Observatory (PBO) network in the contiguous western U.S. identifies multiple shear wave reflections and surface waves that traverse the globe multiple times. This analysis opens up a significant new way to understand the structure of the upper mantle using geodesy.

The July 2019 moment magnitude 6.4 and 7.1 Ridgecrest California earthquakes occurred about 34 hours apart on connected strike-slip faults. Continuous and temporary Global Navigation Satellite Systems (GNSS) sites captured the surface motions during and after the events. The data provides crucial information about how the faults move during and after an earthquake and how this motion is related to other processes, such as plate tectonics and fault creep.

A global model of observed plate motions on Earth’s surface is developed using 19,664 interseismic GPS velocities for 307 distinct plates. The result shows that 50% of the world’s population lives within 200 kilometers of a fault with a slip rate of greater than 2 millimeters per year.

Synthetic Aperture Radar imagery and precipitation data of the Mud Creek landslide in California over 8 years, reveal the catastrophic failure was caused by a large increase in pore-fluid pressure. Satellite imagery is an effective tool for observing landslide behavior.

GPS data and modeling provides the angular velocities for eight blocks and shows that three of the blocks are deforming internally. The model suggests little locking of the Middle America subduction zone, a rheologically weak volcanic arc, and a Central America forearc sliver that moves slowly.

GPS time series and deformation modeling show that the Aira and Kirishima volcanoes are connected at depth. Geodetic observations can be used to determine the structure of volcanoes below the surface and help with hazard preparedness and response.

California’s crustal motions due to plate tectonics, earthquakes, volcanoes, water, humans and other factors occur across many time and space scales. Utilizing geodetic observations over decades, a geodynamic model of these motions explores the cause and effect of past movements, creates a current dynamic model and incorporates the influence of new motions as they occur.

Utilizing 111 geodetic slip distributions for 73 earthquakes with magnitudes from 5.3 to 9.1, fault characteristics are correlated with magnitude. Geodetic data provides a different method to build or enhance empirical relations between magnitude and slip characteristics to improve our understanding of earthquake processes and enhance rapid assessment of earthquake risks and responses.

Analysis of source time functions and geodetic data show that within the first 20 seconds of a magnitude 7+ earthquake, the magnitude can be determined base on the characteristics of the slip pulse. This is a change from previous work regarding determinism or self-similar models of earthquakes. Beyond understanding earthquakes better, the results can help to more quickly determine the size of the event and help with preparedness, response and mitigation.

Examination of borehole strainmeter data for medium size earthquakes (magnitude 4 to 5) in California shows a postseismic moment that is intermediate between small and large earthquakes. This suggests there is a size dependence on the dynamics of earthquakes or on the properties of the fault area around the earthquakes.

A magnitude 7.9 earthquake on 23 January 2018 in the Gulf of Alaska broke multiple orthogonal fault segments. The GNSS data of ground deformation during and after the earthquake showed most of the slip on two west-southwest oriented faults. The earthquake does not appear to have increased the stress in the region of the magnitude 9.2 1964 Alaska earthquake.

Analysis of thousands of GPS observations over decades shows the upward bending of the stable North American plate due to ice loss and horizontal contraction, mostly due to higher than expected inward velocities around the edges of the former ice sheets.

A crustal deformation model for the Western United States fits geodetic and geologic observations and shows where major changes in the crust are occurring. Such modeling is critical for earthquake hazard assessments and for understanding Earth processes.

Analysis of past earthquakes shows that GPS/GNSS sites can provide high-rate, low-noise data to determine peak ground velocities for earthquakes of magnitude greater than 5.8. The geodetic-derived ground motion can help with earthquake early warning, emergency response and earthquake engineering.

A moment magnitude 7.8 earthquake ruptured a major subduction zone boundary between the Nazca and the South American plates just offshore of Ecuador on 16 April 2016. Synthetic aperture radar (SAR) data and model analysis show about 2.5 meters of slip at about 20 kilometers depth. The event implies shorter recurrence times for earthquakes in the region.

An analysis of borehole strainmeter data from Plate Boundary Observatory sites in the western United States for 144 earthquakes from 2004 to 2014 reveals correlations between the peak strain from these events with distance from the hypocenter and the earthquake magnitude.

Analysis of 35 rapid tremor reversals (RTRs) captured by two Plate Boundary Observatory borehole strainmeters near Vancouver Island, British Columbia shows these subevents have high slip rates and modest strain energy release. RTRs contribute a significant fraction of the slow slip moment.

Using GPS and Sentinel 1 radar imagery, the slip along the West Napa fault zone (WNFZ) during and after the 2014 South Napa earthquake was measured. The complexity of the slip and afterslip suggests that hard rock and soft sediment heterogeneity control the style of friction on the fault plane.

The Mw 6.0 South Napa earthquake created measurable surface rupture over about 12 kilometers on several active strands of the West Napa fault zone (WNFZ). Field observations and airborne and satellite-based imagery show earthquake deformation and post-earthquake deformation. The complex fault rupture and post-earthquake fault slip has implications for estimating earthquake hazards.

The San Andreas Fault System (SAFS) has been captured flexing between large earthquakes in southern California with EarthScope’s Plate Boundary Observatory (PBO). The flexure is related to 300 years of fault locking and creeping at different fault depths. Quantifying the flexure will improve estimates of seismic hazard.

The 7 November 2012 moment magnitude 7.4 Champerico (Guatemala) earthquake is among a growing number of subduction zone events observed by a local geodetic network. The GPS data show up to 2 meters of slip over a 30 by 30 square kilometer area on the fault at a depth of 10 to 30 kilometers. The data refine the location of the earthquake, increasing our understanding of faults and plate motions as well as earthquake risk resiliency.

High rate GPS network measurements combined with accelerometer and satellite radar data show that the 25 April 2015 magnitude 7.8 Gorkha Nepal earthquake ruptured a 20-kilometer wide segment of the fault at depth. The rupture propagated toward the Kathmandu basin and the smooth slip onset caused only moderate ground shaking in the city. Greater damage, especially to taller structures in Kathmandu, was caused by whole basin resonance of the seismic waves.

Combined analysis of the seismic and bathymetric data collected along the Aleutian arch of Alaska near Chirikof Island shows a splay fault beneath a subducted ridge. These features suggest the possibility of a earthquake causing a large tsunami that could be directed toward the west coast of the contiguous U.S.. Significantly, the GPS data from Chirikof Island shows that the fault is 90% locked, such that failure in a large earthquake is possible.

Using years of data from the dense geodetic and seismic networks in Japan, researchers find that slow slip events that repeat either coincide or precede large magnitude earthquakes along the major subduction zone off the coast of northeastern Japan.

GPS data combined with Interferometric Synthetic Aperture Radar (InSAR) images characterize the fault and slip distribution for the 24 August 2014 M 6.0 South Napa earthquake. These results show the utility of geodetic data for rapid earthquake response, especially in areas where teleseismic data may not constrain the complexities of damaging events.

Airborne and terrestrial Lidar data of volcanic interior systems in the about 4 million year old San Rafael volcanic field in Utah details 7 sill forming events and 12 conduit forming events. The large volume of shallow sills show that these structures are important for eruption dynamics and inform studies of active volcanoes, particularly their patterns of unrest.

The active plate boundary marked by the Zagros Mountains has high seismicity, a complex fold and fault system and significant hydrocarbon reserves. Analysis of the 18 August 2014 Mw 6.2 Mormori, Iran earthquake with synthetic aperture radar (SAR) satellite imagery shows the event occurred along a shallow, blind thrust fault in the softer sediments above firmer bedrock.

An analysis of geodetic and airborne UAVSAR imagery related to the 2014 M5.1 La Habra earthquake shows that the Los Angeles metro area consists of a complex system of shallow faults that tend to move together during an earthquake. The area shows stored potential of a M6.1–6.3 earthquake using the assumption that the shallow structures released accumulated strain that has not been released on deeper locked structures.

A global model that forecasts the rates of shallow, large-magnitude earthquakes is formulated by combining seismic and geodetic data. Over time, such models can be used by financial experts to develop a catastrophe bond market, providing opportunities for investors, the insurance industry and communities facing significant seismic risks.

A plate tectonic model for the Caribbean is derived using from GPS measurements in the region. Analysis shows the subduction edge of the Caribbean plate transitions from fully locked near Hispaniola to partially locked under Puerto Rico and the Lesser Antilles. This behavior implies about one magnitude 8 earthquake every 2000 years.

Analysis of GPS observations before, during and after the 5 January 2013 Mw 7.5 Craig earthquake show that slip during the earthquake averaged about 6 meters. After the earthquake there was substantial deformation over 1.6 years. The earthquake fills a gap and helps to account for plate motion between the North American and the Pacific plates.

A new method of aligning GPS time series on episodes of small earthquakes has revealed new slow slip events (SSEs) that generate a surface displacement that is below the noise level of typical GPS observations. These results add useful details about the spectrum of fault slip from the subtle to the sublime that can help to understand the probability of future earthquake activity along subduction zones.

Intrusive unrest at Bárðarbunga Volcano in Iceland in 2014 shows segmented lateral dike growth creating new crust where the tectonic plates separate.

The Hayward and Calaveras Faults in the San Francisco East Bay are notable strike-slip systems. New interferometric synthetic aperture RADAR (InSAR) observations and seismicity show the faults are connected. The connection of the faults raises the potential risk of a larger earthquake in a populated region.

The North Anatolian Fault (NAF) is major fault system with a history of large earthquakes that extends across Turkey into the Aegean Sea. Twenty years of GPS observations indicate that the Princes’ Islands fault segment under the Sea of Marmara is the most likely segment to generate a magnitude ~7 earthquake in the future with consequences for Istanbul.

Analysis of GPS observations from 1996 to 2011 show that the northern Tohoku region of Japan was accelerating landward and the south-central Tohoku region was accelerating seaward. The measurements and modeling highlight the value of long term observations of seismic regions and the significance of movement between large earthquakes.

The 2010 magnitude 7.0 Haiti earthquake occurred on a secondary blind thrust fault, the Léogâne fault, rather than on the Enriquillo-Plantain Garden fault (EPGF). The best-fitting model simulation shows that the rupture did not trigger the EPGF or the Trois Baies fault, but there has been significant stress buildup on these faults, so future risks should be considered.

Earthquake hazards along the San Andreas Fault System (SAFS) can be assessed from fault slip rate estimates. A layered earthquake cycle model describes the state of the crust in California and helps to reconcile seemingly disparate geologic and geodetic slip rates. Ultimately a better understanding of earthquakes through such observations and modeling can help reduce risks.

A model of plate motions and strain rates for 50 major tectonic plates that makeup the Earth’s surface has been refined from about 22,500 horizontal geodetic velocities. The new Global Strain Rate Model (GSRM v2.1) details not only plate motions and tectonics, but also can be used as a proxy to the risk of earthquakes within plate boundaries.

The driving forces of the East African Rift System are deciphered by modeling GPS and seismic data of present-day rifting. The models show that density variations within the lithosphere, causing gravitational potential energy (GPE) gradients are driving the current plate spreading in East Africa.

A large number of tracks of mostly hadrosaurid dinosaur footprints discovered in Denali National Park shows that hadrosaurid herds lived in multigenerational groups, that juveniles had relatively rapid growth rates, and that a warm polar world could support a significant population of large plant-eating dinosaurs.

High-resolution LIDAR imaging pinpointed locations for paleoseismic studies at Hazel Dell on the San Andreas Fault. Offset and disturbed sediments provide conclusive evidence of larger magnitudes and amounts of displacement for the historical 1838 and 1890 earthquakes, illuminating the nature of the San Andreas fault system.

On 5 September 2012, a magnitude 7.6 earthquake occurred beneath the Nicoya Peninsula, Costa Rica, where geophysicists had anticipated a possible event and established a strategic observational network before 2012. The observations delineate the earthquake rupture area and refine seismic risk.

Azerbaijan encompasses the eastern Kura basin and the Caucasus Mountains rise on its northern border. Recent geodetic observations suggest a significant strain rate across the Kura basin that may signify a greater seismic risk for Azerbaijan's largest city, Baku.

The magnitude 8.8 Maule Chile earthquake that occurred in 2010 caused subsidence of five volcanic regions in the Andes within weeks of the event. The subsidence was observed via satellite imagery and is attributed to the migration of hydrothermal fluids.

The many tectonic plates that make up the surface of the Earth giving us mountains, earthquakes, volcanoes, coastal plains, seamounts, mid-ocean ridges and other features are tied to flow in the deeper mantle. Global GPS measurements show how the plates move relative to one another and these models can be compared to global dynamic models of mantle flow.

Not only is Iceland spewing out tons of magma from thermal structures, but it also has lots of earthquakes associated with magma and plate movement.

The Yellowstone Plateau Volcanic Field is a very active hotspot and national park with spectacular evidence of volcanic activity on the surface in the form of geysers, hot springs, hydrothermal pools, steaming vents, and seismic activity.

The many tectonic plates that make up the surface of the Earth giving us mountains, earthquakes, volcanoes, coastal plains, seamounts, mid-ocean ridges and other features are tied to flow in the deeper mantle. Global GPS measurements show how the plates move relative to one another and these models can be compared to global dynamic models of mantle flow.

The large earthquakes and tsunamis in Sumatra, Chile, and Japan have accelerated efforts to rapidly determine the location, size, energy, and amount of displacement caused by large earthquakes to assist in response and provide timely warnings of related hazards such as tsunamis.

Isla del Coco, off the coast of Costa Rica, is the only landmass on the Cocos Plate that sits above sea level and thus is the only place where motion of the plate can be measured above the water.

Santorini, a small group of islands located 200 km southeast of mainland Greece, has had a violent past, as evidenced by the collapsed volcanic caldera in its center. The giant Minoan eruption that occurred approximately 3660 years ago may have led to the demise of the Minoan culture, and is responsible for the creation of the large caldera. GPS instruments have been recording the recently renewed activity at Santorini after 60 years of quiescence.

A fountain of lava erupted from a fissure on Kilauea Volcano, Hawaii on March 5, 2011, beginning an eruption that would end four days later. A group of scientists led by Paul Lundgren of the Jet Propulsion Lab have observed the details of this eruption without having to set foot on the volcano using InSAR imagery and UNAVCO GPS station data.