Category Archives: Geology

Antarctica – What’s Under All That Ice?

All Posts, Antarctic, Cartography, Geography, Geology, Global Climate, Remote Sensing, , , , , , , , , ,

Peter Lobner, Updated 24 August 2021

From space, Antarctica gives the appearance of a large, ice-covered continental land mass surrounded by the Southern Ocean.  The satellite photo mosaic, below, reinforces that illusion.  Very little ice-free rock is visible, and it’s hard to distinguish between the continental ice sheet and ice shelves that extend into the sea.

Satellite mosaic image of Antarctica created by Dave Pape, 
adapted to the same orientation as the following maps. 
 Source.  https://geology.com/world/antarctica-satellite-image.shtml

The following topographical map presents the surface of Antarctica in more detail, and shows the many ice shelves (in grey) that extend beyond the actual coastline and into the sea.  The surface contour lines on the map are at 500 meter (1,640 ft) intervals.

Map of Antarctica and the Southern Ocean showing the topography of Antarctica (as blue lines), research stations of the United States and the United Kingdom (in red text), ice-free rock areas (in brown), ice shelves (in gray) and names of the major ocean water bodies (in blue uppercase text).
Source: LIMA Project (Landsat Image Mosaic of Antarctica) via Wikipedia

The highest elevation of the ice sheet is 4,093 m (13,428 ft) at Dome Argus (aka Dome A), which is located in the East Antarctic Ice Sheet, about 1,200 kilometers (746 miles) inland.  The highest land elevation in Antarctica is Mount Vinson, which reaches 4,892 meters (16,050 ft) on the north part of a larger mountain range known as Vinson Massif, near the base of the Antarctic Peninsula.  This topographical map does not provide information on the continental bed that underlies the massive ice sheets.

A look at the bedrock under the ice sheets: Bedmap2 and BedMachine

In 2001, the British Antarctic Survey (BAS) released a topographical map of the bedrock that underlies the Antarctic ice sheets and the coastal seabed derived from data collected by international consortia of scientists since the 1950s. The resulting dataset was called  BEDMAP1.  

In a 2013 paper, P. Fretwell, et al. (a very big team of co-authors), published the paper, “Bedmap2: Improved ice bed, surface and thickness datasets for Antarctica,” which included the following bed elevation map, with bed elevations color coded as indicated in the scale on the left.  As you can see, large portions of the Antarctic “continental” bedrock are below sea level.

Bedmap2 bed elevation grid.  Source:  Fretwell 2013, Fig. 9

You can read the 2013 Fretwell paper here:  https://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf

For an introduction to Antarctic ice sheet thickness, ice flows, and the topography of the underlying bedrock, please watch the following short (1:51) 2013 video, “Antarctic Bedrock,” by the National Aeronautics and Space Administration’s (NASA’s) Scientific Visualization Studio:

NASA explained:

  • “In 2013, BAS released an update of the topographic dataset called BEDMAP2 that incorporates twenty-five million measurements taken over the past two decades from the ground, air and space.”
  • “The topography of the bedrock under the Antarctic Ice Sheet is critical to understanding the dynamic motion of the ice sheet, its thickness and its influence on the surrounding ocean and global climate. This visualization compares the new BEDMAP2 dataset, released in 2013, to the original BEDMAP1 dataset, released in 2001, showing the improvements in resolution and coverage.  This visualization highlights the contribution that NASA’s mission Operation IceBridge made to this important dataset.”

On 12 December 2019, a University of California Irvine (UCI)-led team of glaciologists unveiled the most accurate portrait yet of the contours of the land beneath Antarctica’s ice sheet.  The new topographic map, named “BedMachine Antarctica,”  is shown below.

BedMachine Antarctica topographical map showing the underlying ground features and the large portions of the continental bed that are below sea level.  
 Credit: Mathieu Morlighem / UCI

UCI reported:

  • “The new Antarctic bed topography product was constructed using ice thickness data from 19 different research institutes dating back to 1967, encompassing nearly a million line-miles of radar soundings. In addition, BedMachine’s creators utilized ice shelf bathymetry measurements from NASA’s Operation IceBridge campaigns, as well as ice flow velocity and seismic information, where available. Some of this same data has been employed in other topography mapping projects, yielding similar results when viewed broadly.”
  • “By basing its results on ice surface velocity in addition to ice thickness data from radar soundings, BedMachine is able to present a more accurate, high-resolution depiction of the bed topography. This methodology has been successfully employed in Greenland in recent years, transforming cryosphere researchers’ understanding of ice dynamics, ocean circulation and the mechanisms of glacier retreat.”
  • “BedMachine relies on the fundamental physics-based method of mass conservation to discern what lies between the radar sounding lines, utilizing highly detailed information on ice flow motion that dictates how ice moves around the varied contours of the bed.”

The net result is a much higher resolution topographical map of the bedrock that underlies the Antarctic ice sheets.  The authors note:“This transformative description of bed topography redefines the high- and lower-risk sectors for rapid sea level rise from Antarctica; it will also significantly impact model projections of sea level rise from Antarctica in the coming centuries.”

You can take a visual tour of BedMachine’s high-precision model of Antarctic’s ice bed topography here.  Enjoy your trip.

There is significant geothermal heating under parts of Antarctica’s bedrock

West Antarctica and the Antarctic Peninsula form a connected rift / fault zone that includes about 60 active and semi-active volcanoes, which are shown as red dots in the following map.  

Volcanoes located along the branching West Antarctic Fault/Rift System.
Source:  James Kamis, Plate Climatology, 4 July 2017

In a 29 June 2018 article on the Plate Climatology website, author James Kamis presents evidence that the fault / rift system underlying West Antarctica generates a significant geothermal heat flow into the bedrock and is the source of volcanic eruptions and sub-glacial volcanic activity in the region.  The heat flow into the bedrock and the observed volcanic activity both contribute to the glacial melting observed in the region.  You can read this article here:

http://www.plateclimatology.com/geologic-forces-fueling-west-antarcticas-larsen-ice-shelf-cracks/

The correlation between the locations of the West Antarctic volcanoes and the regions of higher heat flux within the fault / rift system are evident in the following map, which was developed in 2017 by a multi-national team.

Geothermal heat flux distribution at the ice-rock interface superimposed on subglacial topography.  Source:  Martos, et al., Geophysical Research Letter 10.1002/2017GL075609, 30 Nov 2017

The authors note: “Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent-wide heat flux maps have only been derived from low-resolution satellite magnetic and seismological data. We present a high-resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. …. Our high-resolution heat flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice sheet dynamics, and sea level change.”  This Geophysical Research Letter is available here:  

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2017GL075609

The results of six Antarctic heat flux models developed from 2004 to 2017 were compared by Brice Van Liefferinge in his 2018 PhD thesis.  His results, shown below, are presented on the Cryosphere Sciences website of the European Sciences Union (EGU). 

Spatial distributions of geothermal heat flux: (A) Pollard et al. (2005) constant values, (B) Shapiro and Ritzwoller (2004): seismic model, (C) Fox Maule et al. (2005): magnetic measurements, (D) Purucker (2013): magnetic measurements, (E) An et al. (2015): seismic model and (F) Martos et al. (2017): high resolution magnetic measurements.  Source:  Brice Van Liefferinge (2018) PhD Thesis.

Regarding his comparison of Antarctic heat flux models, Van Liefferinge reported:  

  • “As a result, we know that the geology determines the magnitude of the geothermal heat flux and the geology is not homogeneous underneath the Antarctic Ice Sheet:  West Antarctica and East Antarctica are significantly distinct in their crustal rock formation processes and ages.”
  • “To sum up, although all geothermal heat flux data sets agree on continent scales (with higher values under the West Antarctic ice sheet and lower values under East Antarctica), there is a lot of variability in the predicted geothermal heat flux from one data set to the next on smaller scales. A lot of work remains to be done …” 

The effects of geothermal heating are particularly noticeable at Deception Island, which is part of a collapsed and still active volcanic crater near the tip of the Antarctic Peninsula.  This high heat flow volcano is in the same major fault zone as the rapidly melting / breaking-up Larsen Ice Shelf.  The following map shows the faults and volcanoes in this region.  

Key geological features in the Larsen “C” sea ice segment area.  
Source:  James Kamis, Plate Climatology, 4 July 2017
Tourists enjoying the geothermally heated ocean water at Deception Island.  
Source: Public domain

So, if you take a cruise to Antarctica and the Cruise Director offers a “polar bear” plunge, I suggest that you wait until the ship arrives at Deception Island.  Remember, this warm water is not due to climate change.  You’re in a volcano.

For more information on Bedmap 2 and BedMachine:

  • “Antarctic Bedrock,” Visualizations by Cindy Starr,  NASA Scientific Visualization Studio, Released on June 4, 2013:  https://svs.gsfc.nasa.gov/4060
  • Morlighem, M., Rignot, E., Binder, T. et al. “Deep glacial troughs and stabilizing ridges unveiled beneath the margins of the Antarctic ice sheet,” Nature Geoscience (2019) doi:10.1038/s41561-019-0510-8:  https://www.nature.com/articles/s41561-019-0510-8

More information on geothermal heating in the West Antarctic rift / fault zone:

What’s been happening in your neighborhood for the past 750 million years?

All Posts, Cartography, Geography, Geology, , , ,

Peter Lobner

A 15 February 2019 article by Meilan Solly in the Smithsonian online magazine describes a recently released interactive map of the world that shows how the Earth’s continents have moved since 750 million years ago.   With your cursor, you can zoom in and rotate the globe in any direction. Using a pull-down menu at the top center of the screen, you can see the relative positioning of the landmasses at the point in time you selected.  A similar selection box in the upper right corner of the screen allows you to select a particular geological or evolutionary milestone (i.e., first land animals) in Earths’ development.  Even better, you can enter an address in the text box in the upper-left corner of the screen and then see how your selected location has migrated as you explore through the ages.

You can read the Smithsonian article here:

https://www.smithsonianmag.com/smart-news/map-lets-you-plug-your-address-see-how-neighborhood-has-changed-over-past-750-million-years-180971507/

You can directly access the interactive globe here:

http://dinosaurpictures.org/ancient-earth#0

Following are screenshots showing what’s happened to the Lyncean Group’s meeting site in San Diego during the past 750 million years.

I hope you enjoy the interactive globe, with visualization created and maintained by Ian Webster, plate tectonic and paleogeographic maps by C.R. Scotese, and the address search tool by LocationIQ.

Current world map
20 million years ago
66 million years ago – dinosaur extinction
105 million years ago
240 million years ago – Pangea supercontinent
400 million years ago – first land animals.  Looks like the first land animals couldn’t have emerged from the sea in San Diego.
600 million years ago – Pannotia supercontinent
750 million years ago

Antediluvian Continents and Modern Sovereignty Over Continental Seabeds

All Posts, Geography, Geology, , , , , , , ,

Peter Lobner

Ignatius Donnelly was the author of the book, Atlantis: The Antediluvian World, which was published in 1882. I remember reading this book in 1969, and being fascinated by the concept of a lost continent hidden somewhere beneath today’s oceans. While Atlantis is yet to be found, researchers have reported finding extensive continental landmasses beneath the waters of the South Pacific and Indian Oceans. Let’s take a look at these two mostly submerged continents and how improved knowledge of their subsea geography and geology can affect the definition of sovereign maritime zones.

Zealandia

In a 2016 paper entitled, “Zealandia: Earth’s Hidden Continent,” the authors, N. Mortimer, et al., reported on finding a submerged, coherent (i.e., not a collection of continental fragments) continental landmass about the size of India, located in the South Pacific Ocean off the eastern coast of Australia and generally centered on New Zealand. The extent of Zealandia is shown in the following map.

Source: N. Mortimer, et al., “Zealandia: Earth’s Hidden Continent,” GSA Today

The authors explain:

“A 4.9 Mkm2 region of the southwest Pacific Ocean is made up of continental crust. The region has elevated bathymetry relative to surrounding oceanic crust, diverse and silica-rich rocks, and relatively thick and low-velocity crustal structure. Its isolation from Australia and large area support its definition as a continent—Zealandia. Zealandia was formerly part of (the ancient supercontinent) Gondwana. Today it is 94% submerged, mainly as a result of widespread Late Cretaceous crustal thinning preceding supercontinent breakup and consequent isostatic balance. The identification of Zealandia as a geological continent, rather than a collection of continental islands, fragments, and slices, more correctly represents the geology of this part of Earth. Zealandia provides a fresh context in which to investigate processes of continental rifting, thinning, and breakup.”

The authors claim that Zealandia is the seventh largest continental landmass, the youngest, and thinnest. While they also claim it is the “most submerged,” that claim may have been eclipsed by the discovery of another continental landmass in the Indian Ocean.

You can read the complete paper on Zealandia on the Geological Society of America (GSA) website at the following link:

http://www.geosociety.org/gsatoday/archive/27/3/pdf/GSATG321A.1.pdf

Mauritia

In the February 2013 paper, “A Precambrian microcontinent in the Indian Ocean,” authors T. Torsvik, et al., noted that an arc of volcanic islands in the western Indian Ocean, stretching from the west coast of India to the east coast of Madagascar, had been thought to be formed by the Réunion mantle plume (a hotspot in the Earth’s crust) and then distributed by tectonic plate movement over the past 65 million years. Their analysis of ancient rock zircons 660 million to 2 billion years old, found in beach sand, led them to a different conclusion. The presence of the ancient zircons was inconsistent with the geology of the more recently formed volcanic islands, and was evidence of “ancient fragments of continental lithosphere beneath Mauritius (that) were brought to the surface by plume-related lavas.”

The ages of the zircon samples were determined using U-Pb (uranium-lead) dating. This dating technique is particularly effective with zircons, which originally contain uranium and thorium, but no lead. The lead content of a present-day zircon is attributed to uranium and thorium radioactive decay that has occurred since the zircon was formed. The authors also used gravity data inversion (a technique to extract 3-D structural details from gravity survey data) to map crustal thicknesses in their areas of interest in the Indian Ocean.

The key results from this study were:

“…..Mauritius forms part of a contiguous block of anomalously thick crust that extends in an arc northwards to the Seychelles. Using plate tectonic reconstructions, we show that Mauritius and the adjacent Mascarene Plateau may overlie a Precambrian microcontinent that we call Mauritia.”

This paper is available for purchase on the Nature Geoscience website at the following link:

http://www.nature.com/ngeo/journal/v6/n3/full/ngeo1736.html

This ancient continent of Mauritia is better defined in the 2016 article, “Archaean zircons in Miocene oceanic hotspot rocks establish ancient continental crust beneath Mauritius,” by L. Ashwai, et al.. The authors provide further evidence of this submerged continental landmass, the approximate extent of which is shown in the following map.Source: L. Ashwai, et al., Nature Communications

The authors report:

“A fragment of continental crust has been postulated to underlie the young plume-related lavas of the Indian Ocean island of Mauritius based on the recovery of Proterozoic zircons from basaltic beach sands. Here we document the first U–Pb zircon ages recovered directly from 5.7 Ma (million year old) Mauritian trachytic rocks (a type of igneous volcanic rock). We identified concordant Archaean xenocrystic zircons ranging in age between 2.5 and 3.0 Ga (billion years old) within a trachyte plug that crosscuts Older Series plume-related basalts of Mauritius. Our results demonstrate the existence of ancient continental crust beneath Mauritius; based on the entire spectrum of U–Pb ages for old Mauritian zircons, we demonstrate that this ancient crust is of central-east Madagascar affinity, which is presently located ∼700 km west of Mauritius. This makes possible a detailed reconstruction of Mauritius and other Mauritian continental fragments, which once formed part of the ancient nucleus of Madagascar and southern India.”

Starting about 85 million years ago, the authors suggest that the former contiguous continental landmass of Mauritia was “fragmented into a ribbon-like configuration because of a series of mid-ocean ridge jumps,” associated with various tectonic and volcanic events.

You can read the complete article on the Nature Communications website at the following link:

http://www.nature.com/articles/ncomms14086

Implications to the definition of maritime zones

The UN Convention on the Law of the Sea (UNCLOS) provides the basic framework whereby nations define their territorial sea, contiguous zone, and exclusive economic zone (EEZ). These maritime zones are depicted below.

Source: http://continentalshelf.gov/media/ECSposterDec2010.pdf

UNCLOS Article 76 defines the basis whereby a nation can claim an extended territorial sea by demonstrating an “extended continental shelf,” using one of two methods: formula lines or constraint lines. These options are defined below.

Source: http://continentalshelf.gov/media/ECSposterDec2010.pdf

You’ll find more details (than you ever wanted to know) in the paper, “A Practical Overview of Article 76 of the United Nations Convention on the Law of the Sea,” at the following link:

http://www.un.org/depts/los/nippon/unnff_programme_home/fellows_pages/fellows_papers/persand_0506_mauritius.pdf

New Zealand’s Article 76 application

New Zealand ratified UNCLOS in 1996 and undertook the Continental Shelf Project with the firm GNS Science “to identify submarine areas that are the prolongation of the New Zealand landmass”. New Zealand submitted an Article 76 application on 19 April 2006. Recommendations by the UN Commission on the Limits of the Continental Shelf (CLCS) were adopted on 22 August 2008. A UN summary of New Zealand’s application is available here:

http://www.un.org/depts/los/clcs_new/submissions_files/submission_nzl.htm

The detailed CLCS recommendations are available here:

http://www.un.org/depts/los/clcs_new/submissions_files/nzl06/nzl_summary_of_recommendations.pdf

Additional information in support of New Zealand’s application is available on the GNS Science website here:

https://www.gns.cri.nz/static/unclos/

Seychelles and Mauritius joint Article 76 application

The Republic of Seychelles ratified UNCLOS on 16 November 1994 and the Republic of Mauritius followed suit on 4 December 1994. On 1 December 2008, these countries jointly made an Article 76 application claiming continental shelf extensions in the region of the Mascarene Plateau. A UN summary of this joint application is available here:

http://www.un.org/depts/los/clcs_new/submissions_files/submission_musc.htm

The CLCS recommendations were adopted on 30 March 2011, and are available here:

http://www.un.org/depts/los/clcs_new/submissions_files/musc08/sms08_summary_recommendations.pdf

Implications for the future

The recent definitions of the mostly submerged continents of Zealandia and Mauritia greatly improve our understanding of how our planet evolved from a supercontinent in a global sea to the distributed landmasses in multiple oceans we know today.

Beyond the obvious scientific interest, improved knowledge of subsea geography and geology can give a nation the technical basis for claiming a continental shelf extension that expands their EEZ. The new data on Zealandia and Mauritia postdate the UNCLOS Article 76 applications by New Zealand, Seychelles and Mauritius, which already have been resolved. It will be interesting to see if these nations use the new research findings on Zealandia and Mauritia to file new Article 76 applications with broader claims.

Strange Things are Happening Underground

All Posts, Geology, Planetary science, Spacecraft and Missions, , , ,

Peter Lobner

In the last month, there have been reports of some very unexpected things happening under the surface of the earth. I’m talking about subduction plates that maintain their structure as they dive toward the Earth’s core and “jet streams” in the Earth’s core itself. Let’s take a look at these interesting phenomena.

What happens to subduction plates?

Oceanic tectonic plates are formed as magma wells up along mid-ocean ridges, forming new lithospheric rock that spread away from both sides of the ridge, building two different tectonic plates. This is known as a divergent plate boundary.

As tectonic plates move slowly across the Earth’s surface, each one moves differently than the adjacent plates. In simple terms, this relative motion at the plate interfaces is either a slipping, side-by-side (transform) motion, or a head-to-head (convergent) motion.

A map of the Earth showing the tectonic plates and the nature of the relative motion at the plate interfaces is shown below (click on the image to enlarge).

ESRT Page5

Source: http://www.regentsearth.com/

When two tectonic plate converge, one will sink under (subduct) the other. In the case of an oceanic plate converging with a continental plate, the heavier oceanic plate always sinks under the continental plate and may cause mountain building along the edge of the continental plate. When two oceanic plates converge, one will subduct the other, creating a deep mid-ocean trench (i.e., Mariana trench) and possibly forming an arc of islands on the overriding plate (i.e., Aleutian Islands and south Pacific island chains). In the diagram above, you can see that some subduction zones are quite long.

subd_zoneSource: http://www.columbia.edu/~vjd1/subd_zone_basic.htm

The above diagram shows the subducting material from an oceanic plate descending deep into the Earth beneath the overriding continental plate.  New research indicates that the subducting plates maintain their structure to a considerable depth below the surface of the Earth.

On 22 November 2016, an article by Paul Voosen, “’Atlas of the Underworld’ reveals oceans and mountains lost to Earth’s history,” was posted on the sciencemag.org website. The author reports:

“A team of Dutch scientists will announce a catalog of 100 subducted plates, with information about their age, size, and related surface rock records, based on their own tomographic model and cross-checks with other published studies.”

“…geoscientists have begun ….peering into the mantel itself, using earthquake waves that pass through Earth’s interior to generate images resembling computerized tomography (CT) scans. In the past few years, improvements in these tomographic techniques have revealed many of these cold, thick slabs as they free fall in slow motion to their ultimate graveyard—heaps of rock sitting just above Earth’s molten core, 2900 kilometers below.”

The following concept drawing illustrates how a CT scan of the whole Earth might look, with curtains of subducting material surrounding the molten core.

Atlas_1121_1280x720Source: Science / Fabio Crameri

The author notes that research teams around the world are using more than 20 different models to interpret similar tomographic data. As you might expect, results differ. However, a few points are consistent:

  • The subducting slabs in the upper mantle appear to be stiff, straight curtains of lithospheric rock
  • These slabs may flex but they don’t crumble.
  • These two features make it possible to “unwind” the geologic history of individual tectonic slabs and develop a better understanding of the route each slab took to its present location.
  • The geologic history in subducting slabs only stretches back about 250 million years, which is the time it takes for subducting material to fall from the surface to the bottom of the mantle and be fully recycled.

You can read the fill article by Paul Voosen at the following link:

http://www.sciencemag.org/news/2016/11/atlas-underworld-reveals-oceans-and-mountains-lost-earths-history

Hopefully, the “Atlas of the Underworld” will help focus the dialogue among international research teams toward collaborative efforts to improve and standardize the processes and models for building an integrated CT model of our Earth.

A “jet stream” in the Earth’s core

The European Space Agency (ESA) developed the Swarm satellites to make highly accurate and frequent measurements of Earth’s continuously changing magnetic field, with the goal of developing new insights into our planet’s formation, dynamics and environment. The three-satellite Swarm mission was launched on 22 November 2013.

3 satellite SWARMSwarm satellites separating from Russian booster. Source: ESA

ESA’s website for the Swarm mission is at the following link:

http://www.esa.int/Our_Activities/Observing_the_Earth/Swarm/From_core_to_crust

Here ESA explains the value of the measurements made by the Swarm satellites.

“One of the very few ways of probing Earth’s liquid core is to measure the magnetic field it creates and how it changes over time. Since variations in the field directly reflect the flow of fluid in the outermost core, new information from Swarm will further our understanding of the physics and dynamics of Earth’s stormy heart.

The continuous changes in the core field that result in motion of the magnetic poles and reversals are important for the study of Earth’s lithosphere, also known as the ‘crustal’ field, which has induced and remnant magnetized parts. The latter depend on the magnetic properties of the sub-surface rock and the history of Earth’s core field.

We can therefore learn more about the history of the magnetic field and geological activity by studying magnetism in Earth’s crust. As new oceanic crust is created through volcanic activity, iron-rich minerals in the upwelling magma are oriented to magnetic north at the time.

These magnetic stripes are evidence of pole reversals so analyzing the magnetic imprints of the ocean floor allows past core field changes to be reconstructed and also helps to investigate tectonic plate motion.”

Data from the Swarm satellites indicates that the liquid iron part of the Earth’s core has an internal, 420 km (261 miles) wide “jet stream” circling the core at high latitude at a current speed of about 40 km/year (25 miles/year) and accelerating. In geologic terms, this “jet stream” is significantly faster than typical large scale flows in the core. The basic geometry of this “jet stream” is shown in the following diagram.

jet-stream-earth-core-ESA-e1482190909115Source: ESA

These results were published on 19 December 2016 in the article, “An accelerating high-latitude jet in Earth’s core,” on the Nature Geoscience website at the following link:

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2859.html

A subscription is required for access to the full paper.

The Swarm mission is ongoing. Watch the ESA’s mission website for more news.

What Satellite Data Tell Us About the Earthquake in Nepal

All Posts, Geology, Remote Sensing, Spacecraft and Missions, , , , ,

Peter Lobner

A 7.8 magnitude earthquake occurred in the Gorkha region of Nepal on 29 April 2015. A ground displacement map based on data gathered from the Sentinel-1A satellite is shown below. In this image, yellow areas represent uplift and the blue areas represent subsidence.

image Source: ESA

Surface ruptures are places in the ground where the quake has cracked the rock all the way up to the surface. Preliminary satellite data indicate that the Nepal earthquake did not cause any new surface ruptures.

Interferometric analysis of before and after satellite data can be used to measure more subtle changes in the vertical height of the ground along the fault line. Preliminary results from an interferometric analysis by the European Space Agency (ESA), generated from satellite scans of Nepal from April 17 and 29, 2015, is shown in the following image.

image  Source: ESA

Each fringe of color represents 2.8 cm of ground deformation. Areas immediately south of the fault line, like Kathmandu, sank more than a meter into the ground as a result of the quake. Directly north of the fault slip, further into the Himalayas, the ground was lifted up by about a half meter, indicated by the yellow in the first image, above.

Imagine the difficulty of gathering such data from direct physical examination of the affected area.

Read the full article on the Nepal earthquake preliminary satellite data analysis at the following link:

http://www.wired.com/2015/05/satellite-data-tells-us-nepals-brutal-quake/

Read a general article on the use of satellite data to map earthquakes at the following link:

http://www.wired.com/2015/04/turns-satellites-work-great-mapping-earthquakes/

2014 U.S. National Seismic Hazard Model and Induced Seismicity

All Posts, Engineering, Geology, , , ,

Peter Lobner

The U.S. Geologic Society (USGS) National Seismic Hazard Model for the conterminous United States was updated in 2014 to account for new methods, input models, and data necessary for assessing the seismic ground shaking hazard from natural (tectonic) earthquakes. The National Seismic Hazard Maps are derived from seismic hazard curves calculated on a grid of sites across the U.S. that describe the annual frequency of exceeding a set of ground motions. Data and maps from the 2014 U.S. Geological Survey National Seismic Hazard Mapping Project are available for download at the following link:

http://earthquake.usgs.gov/hazards/products/conterminous/

The 2014 maps show higher seismicity in the Eastern U.S. than predicted in previous models. This reflects the significance of the 23 August 2011 magnitude 5.8 earthquake that occurred in Mineral, VA, about 11 miles from the North Anna nuclear power plant. That earthquake was felt as far north as Rhode Island, New York City and Martha’s Vineyard, Mass. The North Anna plant responded well and safely shutdown following the earthquake, which exceeded the plant’s seismic design basis.

The seismic hazard from “potentially induced” earthquakes (I.e., earthquakes that can be associated with man-made activities) was intentionally not considered because there was not a consensus on how to properly treat these earthquakes in a seismic hazard analysis.

The USGS issued a new report on 23 April 2015 examining the sensitivity of the seismic hazard from induced seismicity to five parts of the hazard model: (1) the earthquake catalog, (2) earthquake rates, (3) earthquake locations, (4) earthquake Mmax (maximum magnitude), and (5) earthquake ground motions. In the report, the USGS describes alternative input models for each of the five parts that represent differences in scientific opinions on induced seismicity characteristics.

You can download this interim report for free at the following link:

http://pubs.usgs.gov/of/2015/1070/

The USGS plans to issue a final model after further consideration of the reliability and scientific acceptability of each alternative input model. This matter could have important implications for industries, such as hydraulic fracking and geologic carbon dioxide sequestration, that may contribute to induced seismicity.