publications | Frederick Douglas Pearce

2018

Crustal development within a retreating subduction system: The Hellenides

B.C. Burchfiel, L.H. Royden, D. Papanikolaou, and F.D. Pearce

Geosphere, Mar 2018

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In retreating subduction systems, where the subduction rate is faster than the convergence rate between the upper and lower plates, the processes by which the upper plate crust is constructed have not been well understood. From our studies in the Hellenides, which formed above a retreating slab, we conclude that the external part of the Cenozoic Hellenide orogen was constructed from rocks derived from the subducting plate at least at two crustal levels. The upper crustal level within the external Hellenides consists of west-vergent thrust sheets emplaced progressively from east to west along a regional décollement from ca. 35 Ma to present. These thrust sheets consist of Mesozoic and Cenozoic strata that have been stripped from their underlying basement to form the Hellenides. The middle and lower crustal layer consists of slices of continental crust detached from the downgoing slab at depth and accreted below the upper crustal thrust sheets. These accreted slices represent ∼35% (or less) of the crust belonging to the subducting lithosphere; the remainder of the crust appears to be subducted with the slab. While the process of slab rollback may be continuous at depth, the episodic detachment of crustal slices guarantees that rollback is step-like in time at the crustal level. As the subducted lithosphere rolled back beneath the Hellenides, it passed progressively from east to west through the region occupied by present-day lower crust and mantle, where there is a well-defined Moho. Any irregularities that may have been present at the base of the accreted slabs have been smoothed by processes that remain to be determined.
@article{10.1130/GES01573.1, author = {Burchfiel, B.C. and Royden, L.H. and Papanikolaou, D. and Pearce, F.D.}, title = {Crustal development within a retreating subduction system: The Hellenides}, journal = {Geosphere}, volume = {14}, number = {3}, pages = {1119--1130}, year = {2018}, month = mar, issn = {1553-040X}, doi = {10.1130/GES01573.1}, url = {https://doi.org/10.1130/GES01573.1}, eprint = {https://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/14/3/1119/4181727/1119.pdf} }

2015

Seismic imaging of the western Hellenic subduction zone: the relationship between slab composition, retreat rate, and overriding lithosphere genesis

Frederick Douglas Pearce

Massachusetts Institute of Technology, Mar 2015

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In this dissertation, I investigate the structure and dynamics of the Western Hellenic Subduction Zone (WHSZ) by using two complementary seismic imaging methods and interpreting the resulting images with models that describe the dynamics of retreating subduction. First, I produce high-resolution seismic images across northern and southern Greece using a two-dimensional teleseismic migration method. These images show subducted oceanic crust beneath southern Greece and subducted continental crust beneath northern Greece, with the relative position of the two crusts indicating 70 km of additional slab retreat in the south relative to the north, a result consistent with the predicted relationship between slab buoyancy and retreat rates in recent geodynamic models. Second, I develop a three-dimensional receiver function imaging method, test it with synthetic data, and use it to constrain along strike variations in lithospheric structure. I find a continuous slab Moho across northern and southern Greece between 40 and 80 km depth, with a gentle, trench-parallel component of dip accommodating the observed differential slab retreat. The overriding Moho is deepest beneath the northern Hellenides (35-40 km) and shallowest beneath the Aegean Sea (25-30 km). It also exhibits several characteristics consistent with a retreating subduction model: (1) it is asymmetric when viewed perpendicular to the trench, not symmetric as has been found in previous studies, (2) the location of its leading edge closely tracks the 70 km depth contour of the slab Moho, (3) a well-developed Moho is not observed below the peak topography of the Hellenides, and (4) it exhibits Moho depth fluctuations that are much larger than those predicted assuming surface topography is locally compensated by Airy- Heiskanen isostasy (>+/-4 km). Finally, I combine the seismic-based constraints with those from geologic data and geodynamic models to better understand how the overriding lithosphere is built and deformed during slab retreat. In northern Greece, the overriding crust is found to be predominately built by accretion of slab-derived continental blocks, while in southern Greece the present-day subduction of an oceanic slab domain has caused previously accreted continental blocks to rapidly extend, yielding an asymmetric, valley-shaped pattern in the top of the crystalline basement.
@phdthesis{PearcePhDThesis, title = {Seismic imaging of the western Hellenic subduction zone: the relationship between slab composition, retreat rate, and overriding lithosphere genesis}, author = {Pearce, Frederick Douglas}, numpages = {210}, school = {Massachusetts Institute of Technology}, year = {2015}, url = {https://dspace.mit.edu/handle/1721.1/97259}, eprint = {https://dspace.mit.edu/bitstream/handle/1721.1/97259/910513648-MIT.pdf} }

2014

Evidence of an upper mantle seismic anomaly opposing the Cocos slab beneath the Isthmus of Tehuantepec, Mexico

YoungHee Kim, Hobin Lim, Meghan S. Miller, Fred Pearce, and 1 more author

Geochemistry, Geophysics, Geosystems, Mar 2014

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Subduction of the Cocos plate beneath southern Mexico is characterized by several unusual features, such as a discontinuous volcanic arc, unusual arc chemistry, and anomalously low topography of Tehuantepec Isthmus. Recent seismic images from both receiver functions and seismic tomography suggest that there may be an additional, opposing structure dipping to the southwest from the Gulf of Mexico, and these images have been previously explained by a southwest-dipping slab. However, standard models of the Caribbean tectonic history do not support this interpretation. To better define the Cocos slab’s structure and the possible existence of a structure dipping in the opposite direction, dense seismic data across southern Mexico are used to form high-resolution seismic images, based on the 2-D generalized radon transform method, and to relocate regional earthquakes. Our images show the Cocos plate dipping at 30° to the northeast encounters the anomaly that is dipping in the opposite sense at ∼150 km depth. Relocated seismicity clearly delineates a Wadati-Benioff zone that marks the subducting Cocos plate. A cluster of seismicity also appears at ∼150 km depth which may be related to the subduction of the Tehuantepec ridge and/or to the imaged seismic structure with opposite polarity.
@article{https://doi.org/10.1002/2014GC005320, author = {Kim, YoungHee and Lim, Hobin and Miller, Meghan S. and Pearce, Fred and Clayton, Robert W.}, title = {Evidence of an upper mantle seismic anomaly opposing the Cocos slab beneath the Isthmus of Tehuantepec, Mexico}, journal = {Geochemistry, Geophysics, Geosystems}, volume = {15}, number = {7}, pages = {3021--3034}, keywords = {subduction zone processes, seismic imaging, converted seismic phases, high-precision relocation, seismicity, earthquake clusters}, doi = {https://doi.org/10.1002/2014GC005320}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2014GC005320}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2014GC005320}, year = {2014} }
Pronounced zonation of seismic anisotropy in the Western Hellenic subduction zone and its geodynamic significance

Jean-Arthur Olive, Frederick Pearce, Stéphane Rondenay, and Mark D. Behn

Earth and Planetary Science Letters, Mar 2014

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Many subduction zones exhibit significant retrograde motion of their arc and trench. The observation of fast shear-wave velocities parallel to the trench in such settings has been inferred to represent trench-parallel mantle flow beneath a retreating slab. Here, we investigate this process by measuring seismic anisotropy in the shallow Aegean mantle. We carry out shear-wave splitting analysis on a dense array of seismometers across the Western Hellenic Subduction Zone, and find a pronounced zonation of anisotropy at the scale of the subduction zone. Fast SKS splitting directions subparallel to the trench-retreat direction dominate the region nearest to the trench. Fast splitting directions abruptly transition to trench-parallel above the corner of the mantle wedge, and rotate back to trench-normal over the back-arc. We argue that the trench-normal anisotropy near the trench is explained by entrainment of an asthenospheric layer beneath the shallow-dipping portion of the slab. Toward the volcanic arc this signature is overprinted by trench-parallel anisotropy in the mantle wedge, likely caused by a layer of strained serpentine immediately above the slab. Arcward steepening of the slab and horizontal divergence of mantle flow due to rollback may generate an additional component of sub-slab trench-parallel anisotropy in this region. Poloidal flow above the retreating slab is likely the dominant source of back-arc trench-normal anisotropy. We hypothesize that trench-normal anisotropy associated with significant entrainment of the asthenospheric mantle near the trench may be widespread but only observable at shallow-dipping subduction zones where stations nearest the trench do not overlie the mantle wedge.
@article{OLIVE2014100, title = {Pronounced zonation of seismic anisotropy in the Western Hellenic subduction zone and its geodynamic significance}, journal = {Earth and Planetary Science Letters}, volume = {391}, pages = {100-109}, year = {2014}, issn = {0012-821X}, doi = {https://doi.org/10.1016/j.epsl.2014.01.029}, url = {https://www.sciencedirect.com/science/article/pii/S0012821X14000399}, author = {Olive, Jean-Arthur and Pearce, Frederick and Rondenay, Stéphane and Behn, Mark D.}, keywords = {seismic anisotropy, subduction zones, mantle flow, Aegean, slab rollback, serpentine} }

2012

Seismic investigation of the transition from continental to oceanic subduction along the western Hellenic Subduction Zone

F. D. Pearce, S. Rondenay, M. Sachpazi, M. Charalampakis, and 1 more author

Journal of Geophysical Research: Solid Earth, Mar 2012

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The western Hellenic subduction zone (WHSZ) exhibits well-documented along-strike variations in lithosphere density (i.e., oceanic versus continental), subduction rates, and overriding plate extension. Differences in slab density are believed to drive deformation rates along the WHSZ; however, this hypothesis has been difficult to test given the limited seismic constraints on the structure of the WHSZ, particularly beneath northern Greece. Here, we present high-resolution seismic images across northern and southern Greece to constrain the slab composition and mantle wedge geometry along the WHSZ. Data from two temporary arrays deployed across Greece in a northern line (NL) and southern line (SL) are processed using a 2D teleseismic migration algorithm based on the Generalized Radon Transform. Images of P- and S-wave velocity perturbations reveal N60E dipping low-velocity layers beneath both NL and SL. The ∼8 km thick layer beneath SL is interpreted as subducted oceanic crust while the ∼20 km thick layer beneath NL is interpreted as subducted continental crust. The thickness of subducted continental crust inferred within the upper mantle suggests that ∼10 km of continental crust has accreted to the overriding plate. The relative position of the two subducted crusts implies ∼70–85 km of additional slab retreat in the south relative to the north. Overall, our seismic images are consistent with the hypothesis that faster sinking of the denser, oceanic portion of the slab relative to the continental portion can explain the different rates of slab retreat and deformation in the overriding plate along the WHSZ.
@article{https://doi.org/10.1029/2011JB009023, author = {Pearce, F. D. and Rondenay, S. and Sachpazi, M. and Charalampakis, M. and Royden, L. H.}, title = {Seismic investigation of the transition from continental to oceanic subduction along the western Hellenic Subduction Zone}, journal = {Journal of Geophysical Research: Solid Earth}, volume = {117}, number = {B7}, pages = {}, keywords = {Hellenic subduction zone, continental subduction, orogenic belts, slab rollback, teleseismic imaging}, doi = {https://doi.org/10.1029/2011JB009023}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2011JB009023}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2011JB009023}, year = {2012} }
Seismic imaging of the Cocos plate subduction zone system in central Mexico

YoungHee Kim, Meghan S. Miller, Frederick Pearce, and Robert W. Clayton

Geochemistry, Geophysics, Geosystems, Mar 2012

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Broadband data from the Meso-America Subduction Experiment (MASE) line in central Mexico were used to image the subducted Cocos plate and the overriding continental lithosphere beneath central Mexico using a generalized radon transform based migration. Our images provide insight into the process of subducting relatively young oceanic lithosphere and its complex geometry beneath continental North America. The converted and reverberated phase image shows complete horizontal tectonic underplating of the Cocos oceanic lithosphere beneath the North American continental lithosphere, with a clear image of a very thin low-velocity oceanic crust (7–8 km) which dips at 15–20 degrees at Acapulco then flattens approximately 300 km from the Middle America Trench. Farther inland the slab then appears to abruptly change from nearly horizontal to a steeply dipping geometry of approximately 75 degrees underneath the Trans-Mexican Volcanic Belt (TMVB). Where the slab bends underneath the TMVB, the migrated image depicts the transition from subducted oceanic Moho to continental Moho at ∼230 km from the coast, neither of which were clearly resolved in previous seismic images. The deeper seismic structure beneath the TMVB shows a prominent negative discontinuity (fast-to-slow) at ∼65–75 km within the upper mantle. This feature, which spans horizontally beneath the arc (∼100 km), may delineate the top of a layer of ponded partial melt.
@article{https://doi.org/10.1029/2012GC004033, author = {Kim, YoungHee and Miller, Meghan S. and Pearce, Frederick and Clayton, Robert W.}, title = {Seismic imaging of the Cocos plate subduction zone system in central Mexico}, journal = {Geochemistry, Geophysics, Geosystems}, volume = {13}, number = {7}, pages = {}, keywords = {Mexico, inversion, mantle wedge, oceanic crust, subduction zone, volcanic arc}, doi = {https://doi.org/10.1029/2012GC004033}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2012GC004033}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012GC004033}, year = {2012} }

2009

Inducing in situ, nonlinear soil response applying an active source

Paul A. Johnson, Paul Bodin, Joan Gomberg, Fred Pearce, and 2 more authors

Journal of Geophysical Research: Solid Earth, Mar 2009

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It is well known that soil sites have a profound effect on ground motion during large earthquakes. The complex structure of soil deposits and the highly nonlinear constitutive behavior of soils largely control nonlinear site response at soil sites. Measurements of nonlinear soil response under natural conditions are critical to advancing our understanding of soil behavior during earthquakes. Many factors limit the use of earthquake observations to estimate nonlinear site response such that quantitative characterization of nonlinear behavior relies almost exclusively on laboratory experiments and modeling of wave propagation. Here we introduce a new method for in situ characterization of the nonlinear behavior of a natural soil formation using measurements obtained immediately adjacent to a large vibrator source. To our knowledge, we are the first group to propose and test such an approach. Employing a large, surface vibrator as a source, we measure the nonlinear behavior of the soil by incrementally increasing the source amplitude over a range of frequencies and monitoring changes in the output spectra. We apply a homodyne algorithm for measuring spectral amplitudes, which provides robust signal-to-noise ratios at the frequencies of interest. Spectral ratios are computed between the receivers and the source as well as receiver pairs located in an array adjacent to the source, providing the means to separate source and near-source nonlinearity from pervasive nonlinearity in the soil column. We find clear evidence of nonlinearity in significant decreases in the frequency of peak spectral ratios, corresponding to material softening with amplitude, observed across the array as the source amplitude is increased. The observed peak shifts are consistent with laboratory measurements of soil nonlinearity. Our results provide constraints for future numerical modeling studies of strong ground motion during earthquakes.
@article{https://doi.org/10.1029/2008JB005832, author = {Johnson, Paul A. and Bodin, Paul and Gomberg, Joan and Pearce, Fred and Lawrence, Zack and Menq, Farn-Yuh}, title = {Inducing in situ, nonlinear soil response applying an active source}, journal = {Journal of Geophysical Research: Solid Earth}, volume = {114}, number = {B5}, pages = {}, keywords = {strong ground motion, induced nonlinearity, induced strong ground motion}, doi = {https://doi.org/10.1029/2008JB005832}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2008JB005832}, eprint = {https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008JB005832}, year = {2009} }

2008

Induced Dynamic Nonlinear Ground Response at Garner Valley, California

Zack Lawrence, Paul Bodin, Charles A. Langston, Fred Pearce, and 4 more authors

Bulletin of the Seismological Society of America, Jun 2008

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We present results from a prototype experiment in which we actively induce, observe, and quantify in situ nonlinear sediment response in the near surface. This experiment was part of a suite of experiments conducted during August 2004 in Garner Valley, California, using a large mobile shaker truck from the Network for Earthquake Engineering Simulation (NEES) facility. We deployed a dense accelerometer array within meters of the mobile shaker truck to replicate a controlled, laboratory-style soil dynamics experiment in order to observe wave-amplitude-dependent sediment properties. Ground motion exceeding 1g acceleration was produced near the shaker truck. The wave field was dominated by Rayleigh surface waves and ground motions were strong enough to produce observable nonlinear changes in wave velocity. We found that as the force load of the shaker increased, the Rayleigh-wave phase velocity decreased by as much as ∼30% at the highest frequencies used (up to 30 Hz). Phase velocity dispersion curves were inverted for S-wave velocity as a function of depth using a simple isotropic elastic model to estimate the depth dependence of changes to the velocity structure. The greatest change in velocity occurred nearest the surface, within the upper 4 m. These estimated S-wave velocity values were used with estimates of surface strain to compare with laboratory-based shear modulus reduction measurements from the same site. Our results suggest that it may be possible to characterize nonlinear soil properties in situ using a noninvasive field technique.
@article{10.1785/0120070124, author = {Lawrence, Zack and Bodin, Paul and Langston, Charles A. and Pearce, Fred and Gomberg, Joan and Johnson, Paul A. and Menq, Farn-Yuh and Brackman, Thomas}, title = {Induced Dynamic Nonlinear Ground Response at Garner Valley, California}, journal = {Bulletin of the Seismological Society of America}, volume = {98}, number = {3}, pages = {1412-1428}, year = {2008}, month = jun, issn = {0037-1106}, doi = {10.1785/0120070124}, url = {https://doi.org/10.1785/0120070124}, eprint = {https://pubs.geoscienceworld.org/ssa/bssa/article-pdf/98/3/1412/3673976/1412.pdf} }

2003

Seismic Scattering Attributes to Estimate Reservoir Fracture Density: A Numerical Modeling Study

Frederick Douglas Pearce

Massachusetts Institute of Technology, Jun 2003

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We use a 3-D finite difference numerical model to generate synthetic seismograms from a simple fractured reservoir containing evenly-spaced, discrete, vertical fracture zones. The fracture zones are represented using a single column of anisotropic grid points. In our experiments, we vary the spacing of the fracture zones from 10-meters to 100-meters, corresponding to fracture density values from 0.1- to 0.01-fractures/meter, respectively. The vertical component of velocity is analyzed using integrated amplitude and spectral attributes that focus on time windows around the base reservoir reflection and the scattered wave coda after the base reservoir reflection. Results from a common shot gather show that when the fracture zones are spaced greater than about a quarter wavelength of a P-wave in the reservoir we see 1) significant loss of amplitude and coherence in the base reservoir reflection and 2) a large increase in bulk scattered energy. Wavenumber spectra for integrated amplitude versus offset from the time window containing the base reservoir reflection show spectral peaks corresponding to the fracture density. Frequency versus wavenumber plots for receivers normal to the fractures separate backscattered events that correspond to spectral peaks with positive wavenumbers and relatively narrow frequency ranges. In general, backscattered events show an increase in peak frequency as fracture density is increased.
@mastersthesis{PearceMSThesis, title = {Seismic Scattering Attributes to Estimate Reservoir Fracture Density: A Numerical Modeling Study}, author = {Pearce, Frederick Douglas}, numpages = {37}, school = {Massachusetts Institute of Technology}, year = {2003}, url = {http://hdl.handle.net/1721.1/30127}, eprint = {https://dspace.mit.edu/bitstream/handle/1721.1/30127/55873860-MIT.pdf} }