Ronni Grapenthin

Icelandic rhythmics: Annual modulation of land elevation and plate spreading by snow load

] We find strong correlation between seasonal variationin CGPS time series and predicted response to annual snowload in Iceland. The load is modeled using Green’sfunctions for an elastic halfspace and a simple sinusoidalload history on Iceland’s four largest ice caps. We deriveE = 40 ± 15 GPa as a minimum value for the effectiveYoung’s modulus in Iceland, increasing with distance fromthe Eastern Volcanic Zone. We calculate the elastic responseover all of Iceland to maximum snow load at the ice capsusing E = 40 GPa. Predicted annual vertical displacementsare largest under the Vatnajo¨kull ice cap with a peak-to-peakseasonal displacement of 37 mm. CGPS stations closest tothe ice cap experience a peak-to-peak seasonal displacementof 16 mm, consistent with our model. East and north ofVatnajo¨kull we find the maximum of annual horizontaldisplacements of 6 mm resulting in apparent modulationof plate spreading rates in this area.

Deep magma storage at Hekla volcano, Iceland, revealed by InSAR time series analysis

[1]xa0Hekla volcano is one of the most active volcanoes in Iceland. The most recent eruption occurred from 26 February to 8 March 2000 when about 0.19 km3 of magma was erupted. We present deformation data from multitemporal analyses of synthetic aperture radar (SAR) images acquired between 1993 and 2008, focusing on pixels with low-phase variance (using persistent scatterer and small baseline approaches). Prior to and after the 2000 eruption, we find a broad area of inflation around the volcano (radius about 20 km), with satellite line-of-sight (LOS) shortening of up to 5 mm/yr. We interpret this signal as the result of pressure increase in a deep-seated magma chamber, which we model as a spherical source at 14–20 km depth increasing in volume by 0.003–0.02 km3/yr. Within a ∼6 km radius of the summit of the volcano, a LOS lengthening is superimposed on the broad inflation signal, which correlates partly with recent lava flows. We interpret this signal as the result of thermally contracting lava flows, combined with viscoelastic yielding due to the load of the volcano and its lavas. Coeruptive deflation during the 2000 eruption was similar to the cumulative inflation from 1993 to 2000 and is consistent with a spherical magma chamber at 14–18 km depth that decreases in volume by 0.04–0.08 km3. Interferograms spanning the 2000 eruption show a local coeruptive deformation signal near the eruptive fissure. This is consistent with a dike opening from the surface to depths up to 5.8 km with a volume of 0.005–0.006 km3.

The dynamics of a seismic wave field: Animation and analysis of kinematic GPS data recorded during the 2011 Tohoku-oki earthquake, Japan

[1]xa0During rupture, earthquakes induce permanent and dynamic ground displacements that can be measured by GPS. More than 1200 continuous GPS stations distributed throughout Japan recorded the displacements due to the March 11, 2011, Mw9.0 Tohoku-oki earthquake. We animate these data, which shows the growth of the earthquake rupture over time and illustrates differences of earthquake magnitude through two smaller aftershocks. We also identify dynamic ground motion due to S-waves (body waves), Love waves and Rayleigh waves (surface waves) in this data set. Real time availability of such displacements could be of great use in earthquake response and tsunami warning, and to some degree in earthquake early warning. We find that the length of the ruptured fault can be approximated from displacements which could allow rapid identification of areas prone to large aftershocks. We outline a method that integrates real time displacements into an earthquake alarm system. The animated displacements in map view are easily understandable by specialists and non-specialists alike and hence provide a valuable education and outreach tool.

Pressure sources versus surface loads: Analyzing volcano deformation signal composition with an application to Hekla volcano, Iceland

The load of lava emplaced over periods of decades to centuries induces a gradual viscous response of the Earth resulting in measurable deformation. This effect should be considered in source model inversions for volcanic areas with large lava production and flow emplacement in small centralized regions. If deformation data remain uncorrected, constructive load and pressure source interference may result in an overestimate of depth and volume of a magma reservoir whereas destructive signal interference may cause these values to be underestimated. In both cases the source geometry preference could be biased. The ratio of horizontal and vertical displacements aids the identification of composite signals. We provide a method to quantify and remove the lava load deformation signals, using deformation at Hekla volcano, Iceland as an example.

Computer programing for geosciences: Teach your students how to make tools

When I announced my intention to pursue a Ph.D. in geophysics, some people gave me confused looks, because I was working on a masters degree in computer science at the time. My friends, like many incoming geoscience graduate students, have trouble linking these two fields. From my perspective, it is pretty straightforward: Much of geoscience evolves around novel analyses of large data sets that require custom tools—computer programs—to minimize the drudgery of manual data handling; other disciplines share this characteristic. While most faculty adapted to the need for tool development quite naturally, as they grew up around computer terminal interfaces, incoming graduate students lack intuitive understanding of programing concepts such as generalization and automation. I believe the major cause is the intuitive graphical user interfaces of modern operating systems and applications, which isolate the user from all technical details. Generally, current curricula do not recognize this gap between user and machine. For students to operate effectively, they require specialized courses teaching them the skills they need to make tools that operate on particular data sets and solve their specific problems. Courses in computer science departments are aimed at a different audience and are of limited help.