About

Charles J. Ammon is a Professor and Associate Head for Undergraduate Programs in the Department of Geosciences at Penn State. He earned a B.S. in Physics from Penn State, an M.A. in Geology with a concentration in Geophysics from SUNY Binghamton, and a Ph.D. in Geophysics from Penn State. His research specializes in earthquake seismology, including the development of methods used in seismic imaging of the lithosphere, the study of large- and giant-earthquake rupture processes, and approaches to locating earthquakes along remote mid-ocean ridges. He has been a member of the geoscience faculty since 2001 and has served as Associate Head for Undergraduate Programs since July 2022. Professor Ammon teaches courses on earthquake science to a diverse student body, from non-science majors to advanced geophysics graduate students. He has served on the Board of Directors of the Incorporated Institute of Seismology (IRIS, now part of the EarthScope Consortium), chaired the IRIS Global Seismographic Network Standing Committee, and is a seismic-monitoring advisory committee member for the US Air Force. He is a Fellow of the American Geophysical Union.

Research topics

• Seismology
• Geology
• Geography
• Physics
• Geophysics
• Computer Science
• Optics
• Telecommunications
• Paleontology
• Earth science
• Meteorology
• Mathematics
• Statistics
• Geodesy

Selected publications

• Locating Anthropogenic Seismic Activity at the Redmond Salt Mine

  Seismological Research Letters · 2026-02-18

  articleOpen access

  Abstract We use a nodal seismic network deployed at the Redmond Salt Mine in Utah as a proxy for industrial monitoring to evaluate the efficacy of seismic interferometry for detecting and locating persistent anthropogenic seismic sources. We observe cyclic noise patterns corresponding to mining operations, with distinct stationary and migrating persistent signals. We present an enhanced backprojection location technique to deconvolve source finiteness, better resolving concurrent discrete sources for increased monitoring resolution of anthropogenic activity over time. Our results show that migrating persistent seismic signals consistently focus near lateral blasting areas during evening hours, suggesting they originate from blast preparation activities. In addition, we identify a stationary source near a surface industrial ventilation fan, which likely generates the continuous ground-coupled airwave observed in our data. Our results further demonstrate the utility of seismic interferometry to monitor continuous, high frequency, anthropogenic seismic sources generated by subsurface industrial facilities.

  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 accessCorresponding

  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

• STILGAR: Subsurface Models for Graymont Pleasant Gap Mine

  2025-02-01

  reportOpen access

  The detection, location, and monitoring of underground structures are of great importance to national and global security. Tunnels and voids generate seismic signatures detectable at the surface, but using non-invasive seismic data to image near-surface presents several challenges in real-world applications. In this report, we describe the use of a dense surface seismic deployment to generate subsurface models of the Graymont Pleasant Gap mine - a single-layer mine with a complex structure embedded in a high-velocity P-wave limestone bedrock. Our approach consists of three key methods. We use P-wave arrival times from local blast events to perform a tomography inversion with the tomoTD method, constructing a P-wave velocity model of the subsurface. We model the layer above the mine using Rayleigh wave ellipticity and inversion techniques. We leverage ongoing anthropogenic activities to identify and locate noise sources both on the surface and within the subsurface. With this integrated approach we aim to overcome the challenges and enhance our ability to non-invasively characterize underground structures, contributing to improved seismic monitoring techniques.

  PublisherOA PDFDOI

• STILGAR Seismic Array Data

  OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 2025-01-01

  articleOpen access

  Two three-component dense seismic arrays were deployed above an active limestone mine in Pleasant Gap, Pennsylvania; one in the fall and one in the spring of 2023. Each campaign lasted approximately four weeks and included 80 to 100 seismic stations with stations spaced between 100 and 400 meters apart. Each campaign also included several small dense seismic arrays. Two types of seismic stations were deployed including FairfieldNodal ZLand 3C All-in-One seismometers and Geospace 3C GS-ONE geophone paired with GSX3 and GSX4 dataloggers. This dataset includes ~ 4 TB of three-component continuously recorded seismic data in the miniseed format data from both campaigns as well as a readme file for the data structure.

  PublisherDOI

• Testing the <i>P/S</i> Amplitude Seismic Source Discriminant at Local Distances Using Seismic Events Within and Surrounding the Kloof Gold Mine, South Africa, and the Kiruna Iron Ore Mine, Northern Sweden

  Bulletin of the Seismological Society of America · 2024-03-01 · 5 citations

  article

  ABSTRACT We investigate the utility of the P/S amplitude discriminant for small seismic events recorded at local distances on surface seismic networks using (1) mining-related events from within the Kloof gold mine in South Africa; and (2) mining-related events and earthquakes within and adjacent to the Kiruna iron ore mine in northern Sweden. For the Kloof mine, seventy-five source mechanisms characterized by moment tensor solutions obtained using high-frequency in-mine seismic data are used to evaluate three mine-related source types, isotropic (crush), compensated linear vector dipole (crush-slip), and double-couple (DC; pure slip). For the Kiruna mine region, 270 events are used to evaluate earthquake sources, chemical explosions, and mine-related seismic events (primarily isotropic). For the Kloof mine events, we find that average P/S amplitude ratios measured in the 2–6 Hz frequency band discriminate between isotropic and DC events, and if only pure-slip events with a DC component of &amp;gt;60% are considered, the effective frequency band can be extended from 2 to 8 Hz. For the Kiruna region events, P/S amplitude ratios effectively discriminate earthquakes from chemical explosions in the 4–6 Hz and 10–28 Hz frequency bands. Our findings further show that average P/S amplitude ratios for mine-related events and earthquakes separate at frequencies of 10 Hz and higher. A comparison of amplitude ratios for crush and pure-slip events located within a depth range of 1 km in the Kloof mine, and a comparison of amplitude ratios of shallow (&amp;lt;10 km depth) and deep-focus (&amp;gt;20 km depth) earthquakes in the Kiruna region, indicate that the P/S amplitude discriminant is not influenced significantly by source depth. These findings thus suggest that the P/S amplitude discriminant, originally developed for larger events recorded at regional and teleseismic distances, can be extended to smaller events recorded at local distances.

  PublisherDOI

• Temporal Explosion Source Processes of Declared Nuclear Tests in the Democratic People’s Republic of Korea

  2024-08-30

  reportOpen accessSenior author

  In this work we highlight a preliminary temporal source analysis of the six declared Democratic People's Republic of Korea (DPRK) nuclear tests. We use regional seismic data to estimate relative source time functions (RSTFs) via iterative time-domain deconvolution (Ammon, 2006; Pippin, 2022) of vertical-component ground motions recorded within 2000 km of the source region. Since RSTFs are ideally independent of site and propagation effects, their amplitude spectrum is equivalent to the source spectral ratio, but they also retain phase information. We compare observed RSTFs (in the time and frequency domains) with synthetic RSTFs derived from the Mueller & Murphy (1971) explosion source model. The resolution of these time functions varies, however, we generally obtain high-quality results within the limitations of the recording broadband instrumentation. The results indicate that this method effectively preserves source time-history information that can be used for temporal analysis of remote nuclear explosions. This preliminary analysis is intended to assess the viability of using time-domain deconvolution methods for extracting temporal source information.

  PublisherDOI

• Enhancing Seismic Monitoring for Nonproliferation: Detecting and Tracking Subsurface Mining Activities

  2024-08-01

  reportOpen accessSenior author

  This a presentation for the 2024 Signal Processing Applied to Nonproliferation (SPAN) 2024 workshop. It discusses seismic research conducted at the Redmond Mine as part of the NA-22 STILGAR project. | OSTI.GOV

  PublisherOA PDFDOI

• Detecting Subsurface Mining Activity Using Cross-Correlation and Local Surface Arrays

  2024-04-01

  articleOpen access
  PublisherDOI

• Detecting Anthropogenic Activity at the Pleasant Gap Mine Using Cross-Correlation and Local Surface Arrays

  2024-12-01

  reportOpen access

  This poster summarizes work completed for the NA-22 STILGAR project using seismic cross-correlation to detect human-generated subsurface activity. It will be presented at the 2024 American Geophysical Union Fall Meeting.

  PublisherOA PDFDOI

• Crust and Upper Mantle Structure Beneath the Eastern United States

  Geochemistry Geophysics Geosystems · 2022-03-01 · 15 citations

  articleOpen access

  Abstract The Eastern United States (EUS) has a complex geological history and hosts several seismic active regions. We investigate the subsurface structure beneath the broader EUS. To produce reliable images of the subsurface, we simultaneously invert smoothed P‐wave receiver functions, Rayleigh‐wave phase and group velocity measurements, and Bouguer gravity observations for the 3D shear‐wave speed. Using surface‐wave observations (3–250 s) and spatially smoothed receiver functions, our velocity models are robust, reliable, and rich in detail. The shear‐wave velocity models fit all three types of observations well. The resulting velocity model for the eastern U.S. shows thinner crust beneath New England, the east coast, and the Mississippi Embayment (ME). A relatively thicker crust was found beneath the stable North America craton. A relatively slower upper mantle was imaged beneath New England, the east coast, and western ME. A comparison of crust thickness derived from our model against four recent published models shows first‐order consistency. A relatively small upper mantle low‐speed region correlates with a published P‐wave analysis that has associated the anomaly with a 75 Ma kimberlite volcanic site in Kentucky. We also explored the relationship between the subsurface structure and seismicity in the eastern U.S. We found that earthquakes often locate near regions with seismic velocity variations, but not universally. Not all regions of significant subsurface wave speed changes are loci of seismicity. A weak correlation between upper mantle shear velocity and earthquake focal mechanism has been observed.

  PublisherDOI

Recent grants

• Upgrading the Earthquake Seismology Computing Facility at Penn State

  NSF · $40k · 2005–2008

• Collaborative Research: Northern Embayment Lithosphere Experiment (NELE)

  NSF · $264k · 2011–2017

Frequent coauthors

• Thorne Lay

  University of California, Santa Cruz

  121 shared

• Hiroo Kanamori

  67 shared

• A. A. Velasco

  The University of Texas at El Paso

  43 shared

• R. B. Herrmann

  Saint Louis University

  37 shared

• Stuart A. Sipkin

  35 shared

• S. L. Beck

  32 shared

• Kenji Satake

  The University of Tokyo

  30 shared

• M. Cleveland

  Los Alamos National Laboratory

  30 shared

Education

• Ph.D. , Geosciences / Geophysics

  Pennsylvania State University

Awards & honors

• Fellow of the American Geophysical Union