About

Andrew Nyblade is a Professor of Geosciences affiliated with the Acoustics program at Penn State University. He is part of the Graduate Program in Acoustics, which was founded in 1965 and has become the leading resource for graduate education in acoustics in the United States. The interdisciplinary program offers degrees including Master of Engineering in Acoustics, Master of Science in Acoustics, and Doctor of Philosophy in Acoustics. His contact information includes his office at 447 Deike Building, email aan2@psu.edu, and phone number 814-862-8341. The program is based at Penn State's College of Engineering, located at the 14 Engineering Collaborative Research and Education Building in University Park, PA.

Research topics

• Seismology
• Geology
• Paleontology
• Geophysics
• Geomorphology
• Geography
• Statistics
• Optics
• Mathematics
• Climatology
• Petrology
• Earth science
• Physics

Selected publications

• The structure of Precambrian crust in sub-Saharan Africa: An AfricaArray synthesis and review

  Journal of African Earth Sciences · 2025-04-10

  articleOpen access

  We combine new estimates of crustal thickness and shear wave velocities from 48 broadband seismic stations in Mozambique, Namibia, South Africa and Uganda with previously published results to review and examine Precambrian crustal structure in sub-Saharan Africa for secular trends. The ensemble of crustal structure estimates used relies heavily on data obtained through the AfricaArray initiative, which is briefly reviewed. Whether or not Precambrian crustal structure exhibits notable changes from the Mesoarchean through the Neoproterozoic places a key constraint on continental crustal genesis and evolution. Our 48 new estimates of Moho depth and crustal shear wave velocity profiles, combined with results from similar previous studies, yield an average crustal thickness for all Precambrian terranes of 39 ± 4 km. We find that average crustal thicknesses are essentially identical for Mesoarchean (38 ± 3 km), Neoarchean (39 ± 4 km), Paleoproterozoic (40 ± 4 km), Mesoproterozoic (40 ± 4 km) and Neoproterozoic (39 ± 4 km) terranes. The average thickness of the mafic lower crust, identified by high velocity layering (Vs > 4.0 km/s), is also almost identical in Archean and Proterozoic terranes (7 ± 4 km and 6 ± 4 km, respectively). Finally, the average crustal shear wave velocities for all terranes fall within 1 standard deviation of a mean velocity of 3.7 km/s. These results are consistent with findings from other studies highlighting a lack of evidence for secular variation in crustal structure or composition within Precambrian terranes in sub-Saharan Africa, suggesting that secular trends, if they existed at the time of crust formation, have been obscured by crustal reworking during later orogenic and/or magmatic events.

  PublisherDOI

• Moho depth and sediment thickness estimates for the coastal basins of southeastern Tanzania and the Mozambique Coastal Plain

  Tectonophysics · 2025-04-08

  articleSenior authorCorresponding
  PublisherDOI

• Convolutional Neural Networks Versus <i>P</i>/<i>S</i> Amplitude Ratios in Low-Yield Seismic Event Discrimination: An Evaluation Using Earthquakes, Mine Blasts, and Mining-Related Events from the Kiruna Mining Region, Northern Sweden

  Seismological Research Letters · 2025-04-02 · 2 citations

  article

  Abstract We advance the use of convolutional neural networks (CNNs) for discriminating low-yield seismic events recorded at local distances by evaluating a CNN approach based on time–frequency representations (scalograms) of seismic records from earthquakes, mine blasts, and mining-related seismic events in the Kiruna mining region of northern Sweden to (1) determine if the CNN approach can outperform the P/S amplitude ratio method in classifying these source types, and (2) examine the regional transportability of a CNN model trained on data from the United States. An accuracy of 90% or greater was obtained for the CNN approach for binary source classification between the three source types (earthquakes, mine blasts, and mining-related events), an accuracy level not achieved by the P/S amplitude ratio method, illustrating superior performance of the CNN approach over the amplitude ratio approach. The CNN model trained on explosions and earthquakes in United States yields poor binary classification performance (accuracy &amp;lt; 90%) when applied to earthquakes and mine blasts in the Kiruna mining region, suggesting limited transportability of the U.S.-trained model. However, the poor performance may arise from differences in the blasting style between the two data sets (single-fired borehole explosions in the United States versus ripple-fired blasts into a mine shaft at the Kiruna mine) and source depths (near surface in United States vs. 800–900 m depth in the Kiruna mine), leaving open the question of whether transportability is more limited by differences in local geologic structure or in explosion source processes.

  PublisherDOI

• Observations of Local‐Distance P/S Amplitude Ratios from Deep Mine and Natural Seismic Sources: Implications for Seismic‐Source Discrimination

  Geophysical Prospecting · 2025-07-01 · 1 citations

  articleOpen access

  ABSTRACT For this investigation, we exploit local‐distance P‐ and S‐wave observations generated by mining‐related and small‐magnitude events in the Klerksdorp, Orkney, Stilfontein and Harteesfontein (KOSH) mining region of South Africa to explore the robustness and variability of low‐yield P‐to‐S‐wave amplitude ratios. P/S amplitude ratios are traditionally used in discrimination studies between earthquakes and explosions recorded at regional and teleseismic distances ( 200 km) and for relatively large magnitude events. Few studies have explored the variability of P/S amplitude ratios using data recorded at local distances, distances 200 km, where more scrutiny of wave propagation, near‐surface geology, and source and strain release patterns is required. We took advantage of the dense surface accelerometer cluster network, KOSH, for our variability analysis. Final results show that most of the locally recorded low‐magnitude events in the Klerksdorp region have comparable shear wave energy to low‐magnitude earthquakes. Consequently, our time‐domain rms‐based P and S amplitude measurements result in stable event average P/S ratios likely to separate from explosive sources. We demonstrate the expected variability of the ratios with smaller network simulations (three‐, five‐, seven‐station) to show that ratios remain relatively stable between 1 and 30 Hz.

  PublisherOA PDFDOI

• Investigating Mantle Transition Zone Structure Beneath the Damara Belt in Central Southern Africa Introduction: RF Analysis DI41A-3060

  2025-01-22

  preprintSenior author
  PublisherDOI

• Seismic Evidence for Widespread Active Magmatism in Eastern Marie Byrd Land, Antarctica

  Geophysical Research Letters · 2025-10-05 · 2 citations

  articleOpen access

  Abstract Marie Byrd Land is a volcanically active province that overlaps with the Amundsen Sea Embayment, a region of the West Antarctic Ice Sheet that is experiencing particularly rapid ice mass loss. We locate 34 previously undetected seismic events ( M L 1.2–3.2) and identify 251 additional similar events from 2019 to 2024 in eastern Marie Byrd Land. Located at crustal depths and of magmatic or tectonic origin, these events significantly expand the known geographic extent of such seismicity in West Antarctica. Seismicity is primarily located at Mount Takahe, ∼25 km south of the Crary Mountains, and ∼50 km west of the Kohler Range. Long‐period earthquakes at Mount Takahe have seismic characteristics consistent with active magmatic transport at crustal depths beneath the volcano. Glacio‐volcanic feedback due to ongoing ice mass loss may increase eruption frequency from active Marie Byrd Land volcanic systems, possibly perturbing future ice mass loss rates.

  PublisherOA PDFDOI

• The Pennsylvania State Seismic Network (PASEIS) and Seismicity Within the Commonwealth of Pennsylvania

  Seismological Research Letters · 2025-05-30

  articleSenior author

  Abstract The Pennsylvania State Seismic Network (PASEIS), established to monitor both natural and induced seismic events within the Commonwealth of Pennsylvania, began in 2005 with a limited number of stations and expanded to its current configuration of more than 30 stations in 2016. PASEIS data are recorded continuously and made openly available in near real time under the PE network code via the EarthScope Data Management Center. At Penn State, the data are ingested into the Earthworm software package for automated seismic event detection, location, and magnitude estimation. Earthworm results are reviewed and revised by a seismic analyst and posted to the PASEIS website (see Data and Resources). Between November 2016 and December 2024, 1305 seismic events were detected and located (47 earthquakes, 4 mine collapse events, and 1254 mine and quarry blasting events). During that time interval, no induced events related to hydraulic fracturing or wastewater disposal were detected. The average event magnitude is ML 1.7 for blasts, and analysis of the Gutenberg–Richter relationship suggests magnitude of completeness is ∼1.5 with a b-value of 0.8 for the earthquakes, although limited data makes statistical analysis problematic. The average horizontal epicentral location uncertainty for all events is 1.2 km. By providing open-access data from a statewide network, PASEIS is leading to a greater understanding of seismicity and tectonic stresses within and surrounding Pennsylvania, and thus seismic hazards.

  PublisherDOI

• Mantle Structure Beneath the Damara Belt in South‐Central Africa Imaged Using Adaptively Parameterized P‐Wave Tomography

  Journal of Geophysical Research Solid Earth · 2024-02-26 · 2 citations

  articleOpen access

  Abstract Many seismic tomography studies have indicated that the African Large Low Velocity Province (LLVP) extends from the lower mantle beneath southern Africa into the upper mantle beneath eastern Africa; however, it has been questioned whether the LLVP structure may also extend to the north or northwest beneath south‐central Africa. Debates regarding the upper mantle structure beneath the Damara Belt contribute to this uncertainty. Some studies suggest the Damara Belt is underlain by thermally perturbed upper mantle; however, other studies indicate the region is not associated with anomalous structure. Here, we use a comprehensive P‐wave travel‐time data set and an adaptive model parameterization to develop a new tomographic model for the Damara Belt and surrounding regions. Our results show that seismically slow structure beneath the Damara Belt is relegated to depths greater than ∼1,200 km, indicating that the LLVP is not significantly affecting this region. However, further to the northeast, the LLVP structure obliquely rises and crosses the mantle transition zone near the Irumide Belt, where it then extends into the upper mantle. The seismic structure beneath the Damara Belt and neighboring areas in our model correlates well with tectonic observations at the surface, including variations in heat flow, the distribution of geothermal features, the locations of rifts, and estimates of dynamic topography.

  PublisherOA PDFDOI

• Moment tensors for small earthquakes and the stress regime in the mid-Atlantic United States

  Tectonophysics · 2024-12-02 · 2 citations

  articleSenior author
  PublisherDOI

• Crustal and Uppermost Mantle Azimuthal Seismic Anisotropy of Antarctica From Ambient Noise Tomography

  Journal of Geophysical Research Solid Earth · 2024-01-01 · 4 citations

  articleOpen access

  Abstract Seismic anisotropy provides essential information for characterizing the orientation of deformation and flow in the crust and mantle. The isotropic structure of the Antarctic crust and upper mantle has been determined by previous studies, but the azimuthal anisotropy structure has only been constrained by mantle core phase (SKS) splitting observations. This study determines the azimuthal anisotropic structure of the crust and mantle beneath the central and West Antarctica based on 8—55 s Rayleigh wave phase velocities from ambient noise cross‐correlation. An anisotropic Rayleigh wave phase velocity map was created using a ray—based tomography method. These data are inverted using a Bayesian Monte Carlo method to obtain an azimuthal anisotropy model with uncertainties. The azimuthal anisotropy structure in most of the study region can be fit by a two‐layer structure, with one layer at depths of 0–15 km in the shallow crust and the other layer in the uppermost mantle. The azimuthal anisotropic layer in the shallow crust of West Antarctica, where it coincides with strong positive radial anisotropy quantified by the previous study, shows a fast direction that is subparallel to the inferred extension direction of the West Antarctic Rift System. Fast directions of upper mantle azimuthal anisotropy generally align with teleseismic shear wave splitting fast directions, suggesting a thin lithosphere or similar lithosphere‐asthenosphere deformation. However, inconsistencies in this exist in Marie Byrd Land, indicating differing ancient deformation patterns in the shallow mantle lithosphere sampled by the surface waves and deformation in the deeper mantle and asthenosphere sampled more strongly by splitting measurements.

  PublisherOA PDFDOI

Recent grants

• Collaborative Research: Seismological Investigation of the Cameroon Volcanic Line - A Hot Line in the Mantle?

  NSF · $305k · 2003–2009

• Collaborative Research: Tectonic and Magmatic Processes during Early-Stage Rifting: an Integrated Study of Northern Lake Malawi, Africa

  NSF · $658k · 2012–2018

• Seismic Structure of the Crust and Upper Mantle in the Central and Northern Red Sea Focus Site

  NSF · $104k · 2005–2008

• Collaborative Research: Mantle Structure and Dynamics of the Ross Sea from a Passive Seismic Deployment on the Ross Ice Shelf

  NSF · $266k · 2013–2018

• US-Africa Workshop on Expanding the Africa Array Network to Support Multidisciplinary Science in Africa, Washington, DC

  NSF · $60k · 2010–2011

Frequent coauthors

• Douglas A. Wiens

  Washington University in St. Louis

  168 shared

• R. C. Aster

  Colorado State University

  104 shared

• S. Anandakrishnan

  Pennsylvania State University

  85 shared

• Jordi Julià

  68 shared

• A. D. Huerta

  68 shared

• Raymond Durrheim

  68 shared

• S. E. Hansen

  University of Alabama

  58 shared

• Peter Gerstoft

  Scripps Institution of Oceanography

  51 shared