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[February 18, 2020] New article on NBMG's studies of Walker Lane tectonics and earthquakes!

The Nevada Geodetic Laboratory/Nevada Bureau of Mines and Geology is engaged in new and ongoing work on the Walker Lane in the western Great Basin of the United States. Mike Wolterbeek (UNR) summarized these efforts in a new Nevada Today magazine piece on new efforts and technologies that are being used to read the signs of active crustal deformation in the Walker Lane, and the earthquakes it generates.

[February 10, 2020] NGL Contributes to New Report from the National Academy of Science

Satellite remote sensing is a primary tool for measuring global changes in the land, ocean, biosphere, and atmosphere. Over the past three decades, active remote sensing technologies have enabled increasingly precise measurements of Earth processes, allowing new science questions to be asked and answered. As the demand for measurement precision increases, so does the need for a precise geodetic infrastructure.

Geoffrey Blewitt is co-author on a new report from the National Academy of Science: "Evolving the Geodetic Infrastructure to Meet New Scientific Needs" which summarizes progress in maintaining and improving the geodetic infrastructure. The report identifies improvements to meet new science needs that were laid out in another Academy report "Thriving on Our Changing Planet: A Decadal Strategy for Earth Observation from Space". Focusing on sea-level change, the terrestrial water cycle, geological hazards, weather and climate, and ecosystems, this study examines the specific aspects of the geodetic infrastructure that need to be maintained or improved to help answer the science questions being considered.
Cover of the National Academy Report

[January 30, 2020] M7.7 Earthquake Near the Cayman Islands

On January 28, 2020 a large and shallow strike-slip earthquake occurred at the northern boundary of the Cayman Trough on the Caribbean Sea floor. The event epicenter was between the Cayman Islands, Cuba, and Jamaica, with shaking felt as far away as Florida. GPS data show that stations on the Cayman Islands and Jamaica moved in a fashion consistent with left lateral slip on the fault. The maximum displacement observed was at the UNAVCO-operated COCONet station LCSB which moved over 170 mm to the northwest.

We used rapid orbits from JPL and 5 minute sample rate time series to compute preliminary coseismic offsets. These displacements are depicted on the map below with red vectors for 52 stations. Below the map is an example 5 minute sample rate time series for station LCSB that shows with the red line segment the time interval used to select data to estimate the offsets.
Map of Carwibbean Sea region with vectors showing GPS measured displacements.
GPS Time Series Plot of East, North and Up components for station LCSB

[January 15, 2020] Damaging earthquake sequence in Puerto Rico

A sequence of earthquakes struck southwest Puerto Rico between January 6 and January 11, with at least 8 events over M 5.5 and a main shock with M 6.4. This event poses a challenge for earthquake geodesy because of the difficulty in separating multiple events per day while using precise 24 hour solutions. We simplified our coseismic displacement estimation by solving for a single offset per station on the day of the main shock, January 7, from 24 hour sample rate GNSS solutions using rapid orbit products from the Jet Propulsion Laboratory. The largest offsets observed were over 20 mm, at the NSF-supported Network of the America's station P780, operated by UNAVCO and processed by NGL (station page for P780).
Map of Puerto Rico showing GPS-measured displacements.
The map was made using this a table of preliminary coseismic offsets.

[November 28, 2019] All NGL GPS Holdings Reprocessed and Available in IGS14!

Newly updated GPS data products are now available our online system. All data in the NGL holdings have been reprocessed with the new and improved GipsyX v1.0, software released this year. The new results use improved models including the VMF1 mapping function and nominal troposphere, elevation weighted observations, and higher order ionospheric calibrations, improved JPL Repro 3 orbits, and the latest global reference frame IGS14. Also, time series and MIDAS velocities are now available in 25 tectonic plate fixed reference frames which adjust the horizontal trends only. New station pages have been developed that present these solutions in IGS14, plate fixed reference frames and detrended time series.

Thanks for your patience as we work out the few remaining issues with the web pages.

Happy surfing and Happy Thanksgiving!

[July 7, 2019] Update on M7.1 Ridgecrest Earthquake

Below is an image of the coseismic displacement of the Earth surface that occurred during the M7.1 earthquake near Ridgecrest on July 5, Pacific Time. The maximum movement of a GPS station was over 500 mm, or about half a meter at station P595, about 20 km east of the epicenter. Notably, most of southern California moved because of the event to some degree, though in most places this movement was small, under 10 mm. Similar to the previous M6.4 event on July 4, the movements are approximately east-west extensional, and north-south contractional. This is consistent with right lateral slip on a northwest striking fault plane.

Map of Ridgecrest area showing GPS-measured coseismic displacements.
These data are from several geodetic networks, the largest of which is the Network of the Americas (NOTA), a core component of the NSF Geodetic Facility for the Advancement of Geoscience (GAGE).

The plot is made from this table of preliminary offsets.

[July 6, 2019] M7.1 Earthquake near Ridgecrest, CA

On July 5, one day after the July 4 M6.4 earthquake, an M7.1 event near Ridgecrest, CA generated much larger permanent movement of the Earth surface. For a subset of continuous GPS stations, NGL processes data using JPL's ultra-rapid orbit products, allowing us to calculate coseismic offsets for a few stations on the same day as the earthquake. Results of this ultra rapid analysis are shown below.

We can already see from these early results that the movements are much larger and extend a greater distance than those from yesterday's event. For example, the GPS station GOLD (which is over 70 km southeast of the epicenter) moved ~31 mm, much greater than it moved during yesterday's earthquake (see previous post below). Today's result shows that significant movement extends at least 150 km from the epicenter, and may reach south of the San Andreas Fault. The pattern of the displacements gives us confidence that what we are seeing is from the earthquake. The movement was approximately east-west extensional, and north-south contractional, consistent with the active tectonic strain rate field. The movement is also consistent with the earthquake moment tensor, which along with seismic data, indicate a right lateral strike slip event on an approximately northwest striking plane.

We expect to have results for a much larger number of GPS stations soon.

Map of Ridgecrest area showing preliminary GPS-measured coseismic displacements for M7.1 earthquake

[July 5, 2019] Fourth of July M6.4 Earthquake Near Ridgecrest, California

The map below shows preliminary coseismic horizontal vector displacements for the M6.4 earthquake that occurred near Ridgecrest, California yesterday. The 5 minute sample rate time series were obtained using rapid orbits from the Jet Propulsion Laboratory. Maximum displacements are approximately 10 cm, describing east-west extension and north-south contraction, consistent with a strike-slip event. Four character codes indicate GPS station names. Vectors have 95% confidence ellipses on their tips.

Map of Ridgecrest area with GPS-measured coseismic displacements
The plot was made using this table of preliminary coseismic offsets.

[June 3, 2019] Possible small displacements observed in the Peru M8.0 earthquake

On May 26 an M8.0 earthquake occurred beneath northern Peru. The USGS report on the event indicated the focus was very deep (>110 km) and thus less surface displacement is expected compared to a shallow event. We looked at GPS data from stations within 1585 km of the event and found that stations to the east of the epicenter have a systematic eastward movement, all under 4 mm. The individual offsets are near the uncertainties, but taken together the mean eastward motion may be significant. These results have been rapidly determined, and more more definitive results will be available when more data has been collected after the earthquake.
Map of northern South America showing GPS-measured displacements

[May 24, 2019] New Paper! Drought-Triggered Inflation and Earthquakes at Long Valley Caldera

In a new study we have explored how recent drought periods in California influence the timing of Long Valley active caldera inflation near the city of Mammoth, California. The study uses GPS and seismic data to show how uplift of the Sierra Nevada and magmatic inflation at Long Valley accelerated when the drought initiated in late 2011. The subsequent inflation changed the distribution of active tectonic strain rates in the adjacent central Walker Lane, east of the Sierra Nevada, effecting seismicity rates. Earthquakes occurred more frequently in places where the geodetic strain rates increased, suggesting that hydrological surface loading (e.g. from changing levels of aquifers, snow and lakes) affects the magmatic system in ways that subsequently influence earthquake occurrence. The study captures in new detail the complex links between between climate, active volcanos and earthquakes in eastern California and Nevada.

The work is a collaboration between the Nevada Bureau of Mines and Geology and Department of Mathematics and Statistics in the UNR College of Science. The study appears as a new accepted article in the Journal of Geophysical Research - Solid Earth.
Topographic map of Long Valley with GPS time series, PDSI and GRACE
Hammond, W.C., C. Kreemer, I. Zaliapin, G. Blewitt, 2019, Drought-triggered magmatic inflation, crustal strain and seismicity near the Long Valley Caldera, Central Walker Lane, Journal of Geophysical Research - Solid Earth, 124(6), p. 6072–6091, https://doi.org/10.1029/2019JB017354.

[April 18, 2019] WIRED Article on High Tech Walker Lane Geology Mentions NGL

Space geodesy helps researchers with age old geological conundrums and new theories about the future of the plate boundary according to a new WIRED article on the Walker Lane. Interviews with NBMG scientists Jim Faulds, Bill Hammond and Rich Koehler with writer Geoff Manaugh contribute to this fun, thought provoking piece.


[December 1, 2018] Anchorage Earthquake Coseismic Displacement

Yesterday morning, November 30, 2018, an M 7.0 earthquake struck directly beneath Anchorage, AK causing landslides and widespread shaking. The event was over 40 km deep with a normal slip style mechanism causing some to suggest it was result of a tensional earthquake in the subducting oceanic lithosphere of the Pacific Plate. Here we show that coseismic horizontal displacements were about 2 cm in Anchorage. We obtained these offsets from 5 minute sample rate solutions calculated with JPL rapid orbit products. The horizontal vectors (Figure below) show ESE displacement both east of, and west of, the epicenter. The distance from Anchorage over which displacements are significant extends further east than west. They also show north-south contraction, with stations north of the epicenter moving south, and stations south of the epicenter moving north. Together these observations suggest that the slip occurred on the shallower, down to the east, nodal plane obtained from the seismic data and presented by the USGS.
Map of coseismic displacement from the Anchorage M7.0 earthquake
The rapidly derived coseismic displacents were used to make the figure.

[October 19, 2018] New paper on seasonal strain and seismicity in California and Nevada

The changing amount of water and snow mass that lays on top of the Earth's surface is one possible explanation for observed seasonal variations in seismicity. This hydrological loading would change the state of stress inside the crust minutely with the seasons. We image the seasonal stress variation by using the horizontal seasonal displacements of GPS monuments in the southwestern United States. This reveals large‐scale seasonal patterns of the crust contracting and extending in‐phase with the Earth's surface going down and up, respectively, particularly in northern California which experiences a large excess of water and snow in late winter. The seasonal variations in horizontal deformation there correspond to variations in the number of mainshocks, with more earthquakes occurring when the crust is under extension. In southern California, we see no correlation with the number of mainshocks. In both regions, seasonal deformation correlates with the proportion of large earthquakes and shows an anticorrelation with the aftershock production. So even though seasonal deformation may not directly trigger earthquakes, if an earthquake happens during the right season, it seems to be able to grow a little larger, releasing a little more stress than it otherwise would and reducing the need for (more) aftershocks.

Kreemer, C., and I. Zaliapin, 2018, Spatio-temporal correlation between seasonal variations in seismicity and horizontal dilatational strain in California, Geophysical Research Letters, 45. (18), p. 9559-9568, https://doi.org/10.1029/2018GL079536.


Left panel: Dilatational strain (positive is extension, negative is contraction). Superimposed are the orientations and relative size of the principal axes: white vectors are positive (extensional) and black are negative (contractional). Principal axes reflect spatial averages and for each set the largest axis is normalized to unity. Grey lines are major faults (i.e., with Quaternary slip rate ≡2.5 mm yr-1). Right panel: Vertical displacements inferred from the GPS Imaging technique (Hammond et al., 2016). Superimposed are horizontal displacements (spatially down-sampled) derived from MELD (Kreemer et al., 2018). Numerical results are provided in the paper's Supplemental Information.


[September 24, 2018] NGL publishes new paper in Eos!

Harnessing the GPS Data Explosion for Interdisciplinary Science

More GPS stations, faster data delivery, and better data processing provide an abundance of information benefitting many kinds of Earth science. At NGL we make our data products for over 17,000 stations available online, including metadata, lists of stations, plots of position coordinates, tables of data holdings, and descriptions of new items relating to the products. The service and philosophy, known as Plug and Play GPS , has been documented in a new paper published today in Eos.

NGL is committed to continuing to provide this long-running service to the scientific community, and we encourage researchers to explore these data sets and apply their creative skills to scientific investigations that have yet to be conceived.

Henceforth we request that citation of the data processing and products presented on our website should be:

Blewitt, G., W. C. Hammond, and C. Kreemer (2018), Harnessing the GPS data explosion for interdisciplinary science, Eos, 99, https://doi.org/10.1029/2018EO104623.


Fig. 1. The Nevada Geodetic Laboratory processes data from a global network of about 17,000 geodetic GPS stations.



Fig 2. GPS stations (circles) and observed rate of vertical velocity of continental North America. Glacial isostatic adjustment dominates the field: uplift (red) in Canada and subsidence (blue) in the United States. California’s Central Valley and the Gulf Coast of Texas and Louisiana exhibit rapid subsidence. White regions are statistically consistent with zero motion with respect to Earth’s center of mass. Rates are plotted on a log scale and interpolated using the GPS imaging method of Hammond et al. [2016].


[June 18, 2018] New paper published on the August 24, 2014 M6.0 South Napa Earthquake

A new paper published by Nevada Geodetic Laboratory Graduate Student Meredith Kraner uses data from high‐precision continuous GPS stations to observe a 3 mm horizontal expansion of the Earth's crust prior to and in the vicinity of the August 2014 M6.0 South Napa earthquake. The study is a collaboration with William Holt from Stony Brook University, and Adrian Borsa from Scripps Institution of Oceanography at UC San Diego. The analysis looks at eight years of continuous GPS data leading up to the earthquake and finds that this pattern of horizontal crustal extension repeats every summer. The effect releases pressure on faults in the West Napa fault system, making them more likely to slip during the summer months. We speculate that large seasonal variability in the amount of groundwater in the Sonoma and Napa Valley subbasins may contribute to the observed changes.

Read more in the paper, which has been published in the Journal of Geophysical Research, Solid Earth and is available online
Time series of dilatational strain and Coulomb stress

Also see features from the AGU, AP news, KCBS radio, and Live Science.


[June 14, 2018] Pause in NGL Solutions For IGS14 Upgrade

Owing to the need to transition to IGS14 products as mandated by JPL, our final solutions will cease to be updated with new data until hardware, software, processing and data products systems are updated by sometime later this summer. NGL rapid and ultra-rapid solutions are already in IGS14 and will continue to be available. We are sorry for the inconvenience.


[May 8, 2018] New paper published on glacial isostatic adjustment across North America

The theory of plate tectonics says that tectonic plates move as rigid blocks along the Earth’s surface and that the Earth’s crust should only deform at the boundary between plates. However, the recent explosion in the number of high-precision Global Positioning System stations has allowed us to capture some subtle deformation patterns inside the North American plate that only became apparent by a very careful analysis of the relative motions between thousands of stations. We found that most of the plate is moving at 1-2 mm/yr towards central Canada. Consequently, around most of Canada there is a zone where the crust is contracting. Within Canada, the crust is extending outward and is moving upward rapidly. These patterns can be explained by the process of the crust and mantle still rebounding from a time when it was covered by a thick ice-sheet about 16,000 years ago. The fact that this causes the land to move towards the former ice sheet is an unexpected result that will be useful in understanding the relaxation properties of the underlying mantle. Moreover, we found that earthquakes inside the North American plate do not occur where we see the crust deform, which leaves these events still enigmatic.

The paper is available with open access.

See the UNAVCO Science Snapshot


In the above figure dilatational strain rate with blue and red colors are contractional and extensional, respectively. Results are only shown for dilatation rates that are larger than twice their standard deviation. Superimposed are selected velocities in a reference frame which has the area-weighted mean rotation for the entire plate (i.e., the plate’s net rotation) subtracted from the velocities in the original IGS08 reference frame.


[May 5, 2018] M6.9 Earthquake during volcanic eruptions near Leilani, HI

Yesterday, while volcanic eruptions occurred near the Kilauea East Rift Zone and Leilani, HI, a magnitude 6.9 earthquake occurred in the shallow crust. NGL processes openly available GPS data from continuously operating stations in the area using JPL's GIPSY software and rapid orbit products. Using 5 minute position time series that are automatically produced in our system we were able to estimate coseismic offsets from 57 stations near the epicenter. Many of these stations are near the Kilauea rift zone. We produced a a table of preliminary displacements from these time series.

A figure of these offsets below shows the difference in positions of stations before and after the earthquake, with larger offsets near the event, getting smaller with distance from the epicenter (yellow star). The maximum displacement was 0.77 meters. Gradients in the displacements indicate general extensional strain across the volcanic rift zones.



Data were obtained from continuously operating GPS stations operated by the USGS Hawaiian Volcano Observatory, University of Hawaii, Stanford University, the Jet Propulsion Lab, U.S. Coast Guard, and Federal Aviation Authority.


[February 15, 2018] "GPS Imaging" One of the Most Downloaded JGR Papers in 2017

We were recently notified that our article "GPS Imaging of vertical land motion in California and Nevada: Implications for Sierra Nevada uplift" published in October 2016 was one of the top 10 most downloaded papers in the Journal of Geophysical Research - Solid Earth in 2017! As of year-end 2017 the article received 1456 downloads.

The article is available with open access here: link to JGR.


[January 24, 2018] Update on the M7.9 Alaska Earthquake (see previous story below)

Data from many GPS stations have arrived since the earthquake and these have been processed at NGL using rapid orbits from JPL. We used these data to make 24 hour sample rate time series and estimate coseismic offsets from the difference between the new position and the median position from 10 days before the event. The figure shows that the displacement pattern is consistent with what was found earlier using ultra-rapid orbits. The data now are more numerous and have much smaller uncertaintes. We find that measurable displacement consistent with earthquake deformation is noticeable at many stations over a great distance. For example, INVK which is over 1500 km northeast of the epicenter in Canada's Northwest Territories, appears to have moved several mm to the southwest. Selected station names are given in the figure, offsets with large uncertainites were omitted.


The plot was made using this table of preliminary coseismic offsets.

[January 23, 2018] Massive earthquake offshore southern Alaska

The figure below shows very preliminary coseismic offsets from the January 23, 2018 M7.9 earthquake offshore southern Alaska. These are estimated from 5 minute sample rate GPS time series obtained using ultra-rapid orbit products from the Jet Propulsion Lab, obtained within 15 hours of the event. Only offsets with uncertainties (not shown) less than or equal to 10 mm are included. All resulting offsets are less than 13 mm and so are on the edge of significance. However, the pattern of horizontal motion is consistent with predictions of shallow strike slip event, with southwest displacement in the event’s northeast quadrant and west-northwest displacement in its northwest quadrant.


[December 28, 2017] New paper published on uplift of the Western Transverse Ranges

How fast do mountains grow? What mechanism drives their growth? In Southern California the Western Transverse Ranges experience active tectonic uplift of ~2 mm/yr in response to plate boundary forces contracting the Earth's crust near the Big Bend of the San Andreas Fault. We integrated data from four geodetic techniques (GPS, InSAR, leveling and tide gauges) to map the pattern and rates of uplift and subsidence. The analysis reveals the complexity of vertical land motion, with both tectonic uplift and groundwater aquifer related subsidence contributing the imaged motions. Between the San Andreas fault and Pacific coast, mountain uplift is spatially coherent and consistent with elastic strain accumulation on the region's thrust faults.

Consistency between the space geodetic observations (GPS and InSAR collected over <2 decades) with the terrestrial techniques (leveling and tide gauges which have have been collected over many decades) further suggest that the Western Transverse Ranges uplift signal is tectonic in origin.

Read more in the paper published in the Journal of Geophysical Research - Solid Earth.



[November 5, 2017] - New Data Products Available from the Nevada Geodetic Laboratory!

Nevada Geodetic Lab would like to announce new public availability of over 34,000,000 station-days of tropospheric products (total zenith delay, north gradient, east gradient, every 5 minutes since 1996.0) from over 16,000 stations.

The files have been integrated into our data product system and are available here: ftp://gneiss.nbmg.unr.edu/trop

Those of you familiar with our products already will know we have for many years produced position solutions for a variety of latencies and averaging intervals, from near real-time 5-minute solutions to final 24-hour solutions. These tropospheric products were generated in response to several user requests, and as an unplanned "deliverable of opportunity" for our Plug and Play Project in collaboration with UNAVCO which just came to an end.

Thanks to JPL/Caltech for providing the GIPSY software and orbit and clock products used to generate these solutions, and to the NASA ACCESS Program for support!

[October 30, 2017] - GPS Dark Matter Research Published in Nature Communications

GPS research embraces its dark side! A new paper, published today by a team of researchers from the Nevada Geodetic Laboratory and UNR Physics Department, explores the utility of the GPS system of orbiting satellites to contrain the properties of some of the most enigmatic constituents of the universe. While its existence has been demonstrated, dark matter is incredibly difficult to detect and has never been seen directly with instruments on Earth. Though no actual dark matter was detected, the new paper shows how the atomic clocks on the GPS satellites are being used to place new constraints on dark matter's physical properties. The authorship includes seven UNR co-authors, which include 2 faculty, a post doc, and students.

The manuscript is fully open access,
See also the Nevada Today article,
and Geodetic Science Snapshot at UNAVCO.


[September 19, 2017] - Another large earthquake in Mexico!

Today’s magnitude 7.1 event with epicenter near Raboso, Mexico caused serious shaking, destruction to buildings, and killed over 100 people. The earthquake also permanently shifted the Earth surface enough to offset GPS stations as far away from the epicenter as Mexico City. The plot below, for station MMX1 at the Mexico City airport, was generated using Ultra Rapid orbits from the Jet Propulsion Laboratory. It shows the station moved ~2.2 cm west and 1.6 cm north. These results used less than 2 hours of data after the earthquake as were available on our station webpages shortly thereafter.

Click on the figure for an up to date version of the time series plot. The vertical gray dashed line indicates the time of the event according to the USGS evenet page.


[September 10, 2017] Update on Pijijiapan Earthquake

Since our post yesterday (see below) on the Earthquake in southern Mexico nearly two days of data have been acquired and processed at NGL using rapid orbits from JPL. Time series of 24 hour sample rate positions are providing a greater number of coseismic offsets with greater precision across southern Mexico, and northern Central America. The map below shows vector displacements of GPS stations based on two days of data after the event, compared to the median position of the station from the previous 10 days.

Significant offsets are observed as far east as the Yucatan Peninsula ~1000 km from the epicenter. The offsets show a clear pattern of east-west extension and north-south contraction consistent with the event having a normal-type slip mechanism. Selected station names are given. We used the data to generate a preliminary table of coseismic offsets.

Data used to generate this image were contributed by at least 15 different groups who operate networks and provide open access to GPS data. See this file for a list of data contributors.


[September 9, 2017] Great Earthquake and Tsunami Strike Chiapas and Oaxaca, Mexico

On September 7, 2017 23:49 local time (Sept. 8, 4:49 UTC) a magnitude 8.1 earthquake occurred offshore of the southern Mexican town of Pijijiapan. The event generated a tsunami with waves as high as 1.75 m that were recorded in Chiapas by the Pacific Tsunami Warning Center.

NGL performs daily processing of GPS data from over 8500 stations using rapid orbits from the Jet Propulsion Laboratory, with solutions generally available the following day. Ten stations within several hundred kilometers of the Pijijiapan epicenter provided data for which we were able to generate 5 minute sample rate displacement time series.

Several of these stations recorded significant coseismic offsets from the event. In southern Oaxaca west of the epicenter stations moved westward. The largest movement among these stations was OXUM which moved 7.0+/-0.6 cm westward.

Significant displacement northwest of the epicenter is consistent with what appears from the USGS solutions to be a rupture that propagated northwest from the epicenter.

As more data comes in from GPS stations throughout the region, and processing continues, we will likely be able to obtain a greater number of displacement time series to constrain the slip that occurred in this event.


[May 15, 2017]

New Publication! In a collaboration between the Nevada Geodetic Laboratory and the UNR Mathematics and Statistics Department, Ilya Zaliapin and Corné Kreemer have revisited recent changes in global seismic moment release. Their analysis suggests that the energy released in great earthquaks varies significantly over decades of time, and is not time independent as suggested by some statistical models of earthquake recurrence. Their paper is called "Systematic fluctuations in the global seismic moment release" and has been accepted for Geophysical Research Letters.




[January 18, 2017]

Somewhere around January 4, 2017 our web server went read-only and files were static from that time forward. Upon reboot on January 17, 2017 the disk failed and maintenance was required that continued until January 18, 2017. The system is now restored, time series and plot files are now being refreshed. Thank you for your patience.




[November 13, 2016] Massive Earthquake in New Zealand.

Earlier today,13 November 2016 at 11:02:57 UTC (23:02:57 their local time), a very powerful magnitude 7.8 earthquake rocked New Zealand, south of Wellington. The Nevada Geodetic Laboratory was able to access data from 118 continuously recording GPS stations on the island and estimate coseismic displacements within hours after the event using ultra-rapid orbits from the Jet Propulsion Laboratory. A figure showing a sample of the offsets is given below. The maximum displacements we found with GPS are at station CMBL near Clifford Bay, 1.3 meters east, 2.3 meters north, and 0.9 meters upward. We used the GPS data to make a table of rapidly produced offsets.

While the displacements are very large, they continue to grow as we get more data hour by hour. This likely indicates that a slow but active afterslip on the fault plane, and/or possibly other physical relaxation mechanisms, continue to progress. These observations, along with a continuing sequence of aftershocks, indicates that the crust is still adjusting and evolving as part of this earthquake deformation event. Only GPS stations north of the rupture were strongly affected, which supports seismological evidence that the earthquake ruptured the crust north of the epicenter, where most of the ground shaking occured.

Map of coseismic displacement from New Zealand earthquake

The figure below shows a time series of 5 minute solutions for station KAIK, which had some of the largest displacements.
Time Series for station KAIK


[October 12, 2016] New Paper: GPS Imaging of Sierra Nevada Uplift

Our new paper in JGR Solid Earth shows how our new analysis technique called "GPS Imaging" clarifies the signal of vertical land motion in Nevada and California. Using data from high precision GPS networks we resolve rates and patterns of uplift and subsidence in unprecedented detail. The technique filters the data to enhance underlying signals of vertical movement of the deep solid Earth, which have significance for processes such as mountain growth, earthquake cycle deformation, mantle flow, hydrological mass loading and magmatic systems. A draft of the Hammond et al., 2016 manuscript is now available online with open access here: JGR. Figure 6D from the article below shows the patterns of vertical motion superimposed on the topography. The colors represent vertical rate of the crust (in mm/yr), red up, blue down.

This article was given an Editors’ Highlight at JGR:

"This is the first paper to present such a comprehensive and precise vertical velocity field for a major section of the western United States (Lower 48). It highlights an exciting new method and presents an enormous data set along with its implications. There is a huge amount of data shown in the paper, and there are very interesting implications related to climate change and anthropogenic activity."


[August 29, 2016] M6.2 Earthquake in Central Italy

On August 24, 2016 an M6.2 earthquake hit central Italy near the towns of Norcia and Amatrice causing destruction and loss of ~300 lives. NGL has been routinely processing GPS data from many stations surrounding the effected area. Precise displacements of the solid Earth attributeable to this earthquake have been estimated using rapid orbits from JPL. The plot below shows the differenece in median station position 6 days before and up to 4 days after then event.

The largest offsets are seen at stations NRCI and LNSS which were nearest to the epicenter and moved to the southwest. The pattern of displacement is consistent with a normal faulting event with extension in a SW-NE direction. We used the GPS time series to calculate a preliminary table of coseismic offsets.

We obtained data from stations CAOC, CESI, CONI, GNAL, GUMA, LNSS, MTER, MTTO, ROPI, RSTO, SGRE from the RING network INGV Rome, Italy. Station AQUI from the Euref network. AQRA, CDRA, MRRA, MTRA are from S.I.T.T. Regione Abruzzo. Stations ASCC, CMRN, FOL1, FRMO, GRA8, NRCI, ROIO, TOD2, and TOD3 are from ItalPOS. Stations RIET, TERA, TERI are from the Rete Dinamica Nazionale.




[June 25, 2016] New Publication: Assessing the impact of vertical land motion on 20th century global mean sea level rise

Our new paper in The Journal of Geophysical Research - Oceans [Hamlington et al., 2016] documents the effect of vertical land motion (VLM) as seen throgh the global GPS network has on estimates of global mean sea level (GMSL) rise.

We applied our new GPS Imaging technique to assess the impact of VLM not associated with glacial isostaic adjustment (GIA) on GMSL. Non-GIA VLM results from plate tectonic interactions, matle flow and other processes that change surface elevation slowly over time. We use GPS Imaging to estimate VLM at over 1400 tide gauges, and compare it to estimates from GIA models.

We found that after correcting for GIA effects the tide gauges are on average experiencing positive uplift resulting in an net increase of the GMSL rise estimate by 0.24 +/- 0.08 mm per year. While this result is likely dependent on the subset of tide gauges used and other factors in the corrections, it suggests that non-GIA VLM plays a significant role in 20th century estimates of GMSL.




[June 21, 2016] New Publication: Pre- and post-seismic deformation related to the 2015, Mw7.8 Gorkha earthquake, Nepal

A new paper in Tectonophysics [Gualandi et al., 2016] details an analysis that separates the signals of hydrological loading and tectonics, and solves for the deep alfterslip that occurred following the Gorkha earthquake in Nepal. The results show that in the first 7 months after the event ~15% of the total deformation moment was afterslip, and about 77% of the afterslip moment was silent (not seen in the aftershocks). The paper is open access.


[February 23, 2016] New Publication on Deformation and Faulting in the Central Walker Lane

We have published a new study that clarifies how normal faulting, strike slip faulting, and crustal block rotations work together to accommmodate tectonic deformation within the Central Walker Lane. The manuscript by Jayne Bormann et al. was published in the Earth and Planetary Science Letters, and is now available at the EPSL website.
Central Walker Lane GPS velocities, blocks motions, and fault slip rates.

[February 18, 2016] New Publication and Velocity Fields Available!

We have published a new manuscript in the Journal of Geophysical Research on the MIDAS robust trend estimator. The paper by Blewitt, Kreemer, Hammond, and Gazeaux documents the algorithm used to generate our new online velocity fields. These velocity fields are updated weekly and are available in our data products area (see right side of this page). The manuscript is open access.

University of Nevada, Reno
Last edited 25 February 2020.