Peter LaFemina

Rough crust subduction, forearc kinematics, and Quaternary uplift rates, Costa Rican segment of the Middle American Trench

Orthogonal subduction of bathymetrically rough oceanic lithosphere along the northwestern flank of the Cocos Ridge imprints a distinctive style of deformation on the overriding Costa Rican forearc. We divide the Costa Rican forearc into three 100–160-km-long deformational domains based on the bathymetric roughness and thickness of the Cocos plate entering the Middle American Trench, the dip of the subducting plate, the variation in surface uplift rates of late Quaternary coastal deposits, and the orientations and types of faults deforming Paleogene and Neogene sedimentary rocks. In the ~100-km-long Nicoya domain, coastal deposits show localized surface uplift and arcward tilting above the downdip projections of the fossil trace of the Cocos-Nazca-Panama (CO-NZ-PA) triple junction and the Fisher seamount and ridge. In the ~120-km-long central Pacific forearc domain between the Nicoya Peninsula and Quepos, shallower (~60°) subduction of seamounts and plateaus is accompanied by trench-perpendicular late Quaternary normal faults. Steeply dipping, northeast-striking, margin-perpendicular faults accommodate differential uplift associated with seamount subduction. Uplift and faulting differ between the segments of the forearc facing subducting seamounts and ridges. Inner forearc uplift along the seamount-dominated segment is greatest inboard of the largest furrows across the lower slope. Localized uplift and arcward tilting of coastal deposits is present adjacent to subducting seamounts. In contrast, inboard of the underthrusting aseismic Cocos Ridge, along the ~160-km-long Fila Costena domain between Quepos and the Burica Peninsula, mesoscale fault populations record active shortening related to the ~100-km-long Fila Costena fold-and-thrust belt. The observed patterns of faulting and permanent uplift are best explained by crustal thickening. The uplifted terraces provide a first-order estimate of permanent strain along the forearc in Costa Rica. The permanent strain recorded by uplift of these Quaternary surfaces exceeds the predicted rebound of stored elastic strain released during subduction-zone earthquakes.

Kinematics of the Nicaraguan Forearc from GPS Geodesy

[1] Campaign GPS data from a network in the Nicaraguan forearc show a strong component of arc-parallel motion indicating northwest translation of a nearly rigid forearc sliver. Our measured mean velocity for forearc sites of 15.1 mm yr 1 agrees well with the arc-parallel sliver motion predicted previously by DeMets (2001) derived from closure constraints on oblique convergence between the Cocos and Caribbean plates. The lack of a northeasterly oriented arc-normal component of motion in forearc velocities indicates that there are complexities involved beyond a simple interpretation of sliver motion being driven by oblique convergence. The forearc is reasonably well-fit by rigid rotation about an Euler pole with a rms misfit of residual velocities of 4.9 ± 2.6 mm yr 1 . Current motion of the forearc sliver relative to the stable Caribbean plate yields predominantly boundary parallel NW motion with boundary normal extension in the northwestern region averaging 5m m yr 1 . Citation: Turner, H. L., III, P. LaFemina, A. Saballos, G. S. Mattioli, P. E. Jansma, and T. Dixon (2007), Kinematics of the Nicaraguan forearc from GPS geodesy,Geophys. Res. Lett., 34, L02302, doi:10.1029/2006GL027586.

Volcano deformation at active plate boundaries: Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland

Volcano deformation at active plate boundaries: Deep magma accumulation at Hekla volcano and plate boundary deformation in south Iceland

Kinematics of the western Caribbean: Collision of the Cocos Ridge and upper plate deformation

Subduction of the Cocos plate and collision of the Cocos Ridge have profound effects on the kinematics of the western Caribbean, including crustal shortening, segmentation of the overriding plate, and tectonic escape of the Central American fore arc (CAFA). Tectonic models of the Panama Region (PR) have ranged from a rigid block to a deforming plate boundary zone. Recent expansion of GPS networks in Panama, Costa Rica, and Colombia makes it possible to constrain the kinematics of the PR. We present an improved kinematic block model for the western Caribbean, using this improved GPS network to test a suite of tectonic models describing the kinematics of this region. The best fit model predicts an Euler vector for the counterclockwise rotation of the CAFA relative to the Caribbean plate at 89.10°W, 7.74°N, 1.193° Ma−1, which is expressed as northwest-directed relative block rates of 11.3 ± 1.0–16.5 ± 1.1 mm a−1 from northern Costa Rica to Guatemala. This model also predicts high coupling along the Nicoya and Osa segments of the Middle American subduction zone. Our models demonstrate that the PR acts as a single tectonic block, the Panama block, with a predicted Euler vector of 107.65°W, 26.50°N, 0.133° Ma−1. This rotation manifests as northeast migration of the Panama block at rates of 6.9 ± 4.0–7.8 ± 4.8 mm a−1 from southern Costa Rica to eastern Panama. We interpret this motion as tectonic escape from Cocos Ridge collision, redirected by collision with the North Andes block, which migrates to the northwest at 12.2 ± 1.2 mm a−1.

A complex earthquake sequence captured by the continuous GPS network in SW Iceland

A complex sequence of earthquakes struck the western part of the South Iceland Seismic Zone (SISZ) on 29 May 2008. The sequence initiated with a M(w)6.3 (NEIC) earthquake in the western part of the SISZ. Aftershocks from the earthquake delineate two parallel N-S trending structures 4 km apart, in addition to activity along an E-W zone further westward. Continuous GPS measurements can best be explained by right-lateral strike-slip motion on two parallel N-S trending faults, with little slip occurring on other structures illuminated by earthquake activity. We estimate a total moment release of M(w)6.2, with M(w)6.1 on the first rupture and M(w)6.0 on the second rupture. High rate (1 Hz) CGPS data from a near-field station suggest that the main asperity on the Kross fault ruptured within 3 s of the initial mainshock on the Ingolfsfjall fault. Citation: Hreinsdottir, S., T. Amadottir, J. Decriem, H. Geirsson, A. Tryggvason, R. A. Bennett, and P. LaFemina (2009), A complex earthquake sequence captured by the continuous GPS network in SW Iceland, Geophys. Res. Lett., 36, L12309, doi: 10.1029/2009GL038391.

A new sulfur and carbon degassing inventory for the Southern Central American Volcanic Arc: The importance of accurate time-series datasets and possible tectonic processes responsible for temporal variations in arc-scale volatile emissions

This work presents a new database of SO2 and CO2 fluxes from the Southern Central American Volcanic Arc (SCAVA) for the period 2015-2016. We present ∼300 SO2 flux measurements from 10 volcanoes and gas ratios from 11 volcanoes in Costa Rica and Nicaragua representing the most extensive available assessment of this ∼500 km arc segment. The SO2 flux from SCAVA is estimated at 6,240±1,150 T/d, about a factor of three higher than previous estimations (1972-2013). We attribute this increase in part to our more complete assessment of the arc. Another consideration in interpreting the difference is the context of increased volcanic activity, as there were more eruptions in 2015-2016 than in any period since ∼1980. A potential explanation for increased degassing and volcanic activity is a change in crustal stress regime (from compression to extension, opening volcanic conduits) following two large (Mw>7) earthquakes in the region in 2012. The CO2 flux from the arc is estimated at 22,500±4,900 T/d, which is equal to or greater than estimates of C input into the SCAVA subduction zone. Time-series datasets for arc degassing need to be improved in temporal and spatial coverage to robustly constrain volatile budgets and tectonic controls. Arc volatile budgets are strongly influenced by short-lived degassing events and arc systems likely display significant short-term variations in volatile output, calling for expansion of nascent geochemical monitoring networks to achieve spatial and temporal coverage similar to traditional geophysical networks.

Continuous subsidence in the Thingvellir rift graben, Iceland: Geodetic observations since 1967 compared to rheological models of plate spreading

North America-Eurasia relative plate motion across the Mid-Atlantic Ridge in south Iceland is partitioned between overlapping ridge segments, the Western Volcanic Zone (WVZ) and the Eastern Volcanic Zone. The Thingvellir graben, a 4.7 km wide graben, lies along the central axis of the WVZ and has subsided >35 m during the Holocene. An ~8 km long leveling profile across the graben indicates a subsidence rate of ~1 mm yr−1 from 1990 to 2007, relative to the first (westernmost) benchmark. Modeled GPS velocities from 1994 to 2003 estimate a spreading rate of 6.7 ± 0.5 mm yr−1 or 35% of the full plate motion rate and up to 6.0 mm yr−1 subsidence. The combined geodetic observations show that the deformation zone is 10 times wider than the graben width. We utilize these geodetic observations to test the effects of ridge thermal structure on the kinematics across divergent boundaries. We apply a nonlinear rheology, thermomechanical model implemented in a finite element model. A 700°C isotherm is applied for the brittle to ductile transition in the crust, representing a dry olivine rheology. We adjust the depth of this isotherm to solve for the best fit model. The best fit model indicates that the 700°C isotherm is at 8 km depth below the ridge axis, which results in an average thermal gradient of 87.5°C km−1 in the upper crust. The thermomechanical model predicts a subsidence rate of 4 mm yr−1, comparable to our geodetic observations.

Plate Tectonics and Volcanism

Plate tectonics is the paradigm in the Earth system science that links solid Earth processes acting within and on the surface of the Earth with processes that have lead to the evolution of the atmosphere and hydrosphere. The processes and phenomena that connect these parts of the Earth system are driven by magmatism and volcanism. This link is much stronger than the classic correlation between plate tectonic boundary type (i.e., convergent or divergent boundaries), magma generation, and volcanic phenomena acting on millennial or greater timescales. Magmatic and tectonic systems interact at timescales of seconds to years, leading to the triggering of volcanic eruptions by large magnitude earthquakes, and earthquakes by magmatic activity.

iVR for the geosciences

Field trips are an essential part in many disciplines taught in K12 STEM (Science, Technology, Engineering, and Math) education inside and outside the US such as geography, geosciences, and architecture. Field trips foster embodied experiences of places where students can be situated into an informal learning environment. However, field trips are underutilized due to numerous constraints, a situation that current mass development in immersive technologies promises to eliminate. This paper presents an educational project that aims at creating and empirically evaluating virtual reality (VR) experiences for the geosciences: an interactive volcano experience based on LiDAR (Light Detection And Ranging) and image data of Icelands Thrihnukar volcano. This work-in-progress prototype addresses the lack of content and tools for immersive virtual reality (iVR) in geoscientific education and research and how to make it easier to integrate iVR into classroom experiences. It makes use of environmentally sensed data such that interaction and linked content can be integrated into a single experience. We discuss our workflows as well as methods and authoring tools for iVR analysis and creation of virtual educational experiences. These methods and tools aim to enhance the utility of geospatial data from repositories such as OpenTopography.org through unlocking treasure-troves of geospatial data for VR applications. Their enhanced accessibility in education and research for the geosciences and beyond will benefit geoscientists and educators who cannot be expected to be VR and 3D application experts.

Understanding magmatic processes at Telica volcano, Nicaragua: crystal size distribution and textural analysis

Abstract Telica volcano in Nicaragua currently exhibits persistent activity with continuous seismicity and degassing, yet it has not produced lava flows since 1529. To provide insight into magma chamber processes including replenishment and crystallization, crystal size distribution (CSD) profiles of plagioclase feldspar phenocrysts were determined for Quaternary Telica basalts and basaltic andesites. Textural analysis of 14 highly crystalline lavas (>20 vol% phenocrysts) indicates that the samples are dominated by sieve-textured plagioclase feldspar phenocrysts whose origin requires thermochemical disequilibrium within the magmatic system. The CSD curves display an inverse relationship between phenocryst length and population density. Concave-up patterns observed for the Telica lava samples can be represented by linear segments that define two crystal populations: a steeply sloping segment for small crystals (<1.5 mm) and a gently sloping segment for crystals >1.5 mm in length. The two crystal populations may be explained by magma replenishment and a mixing model in which a mafic magma is introduced to a stable chamber that is petrologically and geochemically evolving. Residence times calculated using the defined linear segments of the CSD curves suggest these magmatic processes occur over timescales on the order of decades to centuries. The crystal size distribution and textural analysis advocate for the current persistent activity as being consistent throughout Telica’s historic and prehistoric eruptive periods and driven by replenishment of mafic magma.