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Article

Experimental Seismic Surveying in a Historic Underground Metals Mine

by
John H. McBride
1,*,
Lex Lambeck
2,
Kevin A. Rey
1,
Stephen T. Nelson
3 and
R. William Keach
1
1
Department of Geological Sciences, Brigham Young University, Provo, UT 84602, USA
2
MAG Silver, Vancouver, BC V6C 1B4, Canada
3
Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA
*
Author to whom correspondence should be addressed.
Geosciences 2025, 15(6), 221; https://doi.org/10.3390/geosciences15060221
Submission received: 4 May 2025 / Revised: 1 June 2025 / Accepted: 9 June 2025 / Published: 12 June 2025
(This article belongs to the Section Geophysics)
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Abstract

Underground mine surveys present unique challenges, including the logistics of deploying an energy source, placing geophones in solid rock, managing reverberation from the adit, and ensuring safety. We present the results of seismic surveying at the historic Deer Trail Mine in south-central Utah (USA). The mine is located along the eastern side of the Tushar Range. The surveys utilised a narrow, mostly horizontal adit, 120–510 m below the ground surface. The country rock consists of highly fractured and mineralised Permian to Pennsylvanian quartzites, shales, and limestones. A short test of a 96-channel common midpoint (CMP) P-wave profile was conducted using an accelerated weight-dropper source. We supplemented the P-wave survey with tests of surface-wave dispersion and horizontal-vertical spectral ratio modelling for shallow S-wave structure. These tests confirmed the capability to map shallow, small-scale structure. A conventional CMP 264-channel survey with an explosive source covered 1728 m. A static recording array was used for both surveys with 4.5-Hz vertical geophones. The conventional CMP profile imaged horizontal and dipping reflectors down to about 2000 m, interpreted as lithologic variations in the bedrock. Our study demonstrates the potential for high-resolution seismic exploration in an unconventional and challenging setting to guide the exploitation of deeply buried mineral resources.

1. Introduction

Deep underground mining can be challenged by a lack of geological context within the country rock that surrounds a narrow tunnel. Underground geophysical surveys have the potential to extend sparse geological observations within a tunnel or extrapolated from the ground surface above the tunnel; however, few studies of underground geophysical surveys, especially using controlled-source seismic methods [1,2], have been published. Underground surveys present challenges and hazards beyond those of conventional surface seismic surveying. These include drilling of shot holes in hard rock, detonation of explosives, emplacement of geophones within or over fractured bedrock, laying out of long geophone and interface cables along the narrow margin of a tunnel, and designing a communication system for remote triggering of detonation by the seismograph recording system.
Numerous studies have reported on surface seismic surveys above tunnels or planned tunnel sites [1,2,3,4,5] and over underground mines or planned mining sites [6,7,8]. For example, Ref. [5] reviews the use of several combined geophysical methods, including seismic reflection, refraction, and surface wave dispersion, to refine a model of the subsurface for planning or exploring a tunnel. They discuss several case studies of tunnel-site exploration in the context of safety and risk mitigation. Seismic surveying inside underground mines has become more common over the past two decades (e.g., salt, coal, precious metals) [4,9,10,11,12,13,14,15,16,17,18]. In the Kambalda region of Western Australia, Refs. [4,11] detail the technical aspects of underground seismic exploration of the Hunt metals mine. A pioneering study of seismic methods applied in an underground potash mine in Canada [9] demonstrates the potential of acoustic imaging in a challenging environment. The results of these studies indicate the difficulties of conducting a seismic survey deep underground, imaging in rocks that may be highly recrystallised with only small acoustic impedance contrasts, and encountering unusual noise conditions in a narrow tunnel.
This paper presents the results of an experimental set of seismic surveys conducted in a deep underground metals mine in south-central Utah, USA (Figure 1). The specific objectives are (1) to test the potential of four seismic methods applied underground in a challenging environment for geophysical imaging of the subsurface; (2) to assess the success of each method independently of the others; (3) to explore how best to integrate results from the four methods to enhance our understanding of the bedrock structure beneath the mine tunnel.

2. Geologic Setting

The study area for the Deer Trail mine is centred in the Marysvale volcanic field [20], located in west-central Utah (USA), in the Transition Zone between the Basin and Range and Colorado Plateau Provinces to the west and east, respectively (Figure 1). The Deer Trail mine is one of the few metal mines in the western USA that remains completely dry and is ideally configured to allow for underground geophysical surveys within a long, mostly flat, and straight tunnel. The Deer Trail ore body was discovered in 1878 by deer hunters [21] and has been mined intermittently since then for lead, zinc, silver, gold, and copper. The ore body is a carbonate replacement deposit hosted in the lower part of the Early Permian Toroweap Formation [22]. The deposits developed as a group of elongated, semi-continuous strata-bound bodies (“mantos”, i.e., with shapes like a blanket or cylinder) in carbonate beds associated with fracture-controlled feeder zones [11].
The Deer Trail Mine adit opens about 360 m east of the mapped Tushar Mountains normal fault on its downthrown side [23] (Figure 1 and Figure 2) and continues underground eastward beneath the Tushar Mountains into the PTH tunnel (Figure 2). This tunnel was opened in 1945 to extend exploration of the Deer Trail orebody. Surface geology near the adit and into the PTH tunnel consists of Middle Pleistocene and Holocene alluvial fan deposits (Figure 2a,b). The tunnel lies beneath, from the land surface downward, the northwest-dipping Lower Triassic Moenkopi Formation (mainly sandstone, shale) and the Permian Kaibab and Early Permian Toroweap Formations (mainly limestone). From east to west, the PTH tunnel penetrates a poorly consolidated slump zone of Quaternary talus deposits, then the northwest-dipping Permian Queantoweap Sandstone, Permian Pakoon Dolomite, and Pennsylvanian Callville Limestone [11,22]. The Callville Limestone dips to the west and lies mainly beneath the tunnel. The Mississippian Redwall Limestone lies stratigraphically beneath the Callville Limestone below the tunnel. The tunnel is cut by multiple normal faults in the footwall (i.e., west) of the Tushar Mountain normal fault (Figure 2). The displacement along the faults mainly pre-dates mineralisation, although there may occasionally be several metres of displacement following mineralisation.
The adit is inclined 2 degrees eastward toward the portal and is mostly straight with minor dog-leg bends (Figure 2). The total length of the tunnel is approximately 2570 m. The section of the tunnel used for seismic surveys is narrow (~3 × 3 m) (Figure 3a,b and Figure 4) and lies 120–510 m below the ground surface, deepening toward the west beneath the east slope of the Tushar Mountains (Figure 1 and Figure 2). For the seismic surveys, we selected the section of the tunnel west of the alluvial talus deposits to ensure the survey line was surrounded by the mineralised host rock (Figure 3). The tunnel invert is underlain by 1–2 m of gravel or crushed country rock with an old narrow-gauge rail installed.

3. Methods

3.1. Seismic Acquisition Methods

Due to the lack of established seismic surveying practices in deep underground metals mines, our study adopted an experimental approach. We utilised four seismic methods: (1) a short test high-resolution common mid-point (CMP) compressional (P) wave high-resolution seismic reflection profile; (2) a coincident multi-channel analysis of surface waves (MASW) survey for shear (S) wave velocity inversion; (3) an extended P-wave conventional seismic CMP profile; and (4) test horizontal-to-vertical spectral ratio (HVSR) soundings.

3.1.1. Short Test P-Wave High-Resolution CMP and MASW S-Wave Velocity Profile

The short test high-resolution CMP profile was first surveyed at the east end of the area of interest in the tunnel (Figure 2) to evaluate the feasibility of shorter station spacings. The source was a 45-kg accelerated elastic weight dropper [25], modified for deployment along the old narrow-gauge rail line in the mine (Figure 4), and field-stacked three times. For this profile, a 3.05-m source and receiver interval was utilised. Based on an assumed minimum P-wave velocity of 2000 m/s and an anticipated recorded signal with a maximum frequency of 150 Hz (likely an overestimate), using the relation between receiver/source interval, velocity, and frequency (interval is less than or equal to minimum velocity divided by twice the maximum frequency [26]) yields a maximum interval of about 7 m. Furthermore, steep geologic dips were not expected in the bedrock stratigraphy [20,21], negating the need for finer receiver spacing. The static receiver array included 96 channels, with the source starting and ending 24 channels (73.2 m) outside the “walk-through” array, to build up the CMP fold of cover in the stacked section, which provided 363 m of coverage with a maximum fold of cover of 96. Vertical 4.5-Hz geophones were employed with a sample rate of 0.5 ms and a record length of 3 s. No field filters were applied so that the records would preserve a fuller bandwidth for Rayleigh waves and thus could also be used for MASW. The MASW shear-wave velocity model spanned approximately 215 m within the CMP profile coverage. The tunnel elevation over the length of the short test survey remained roughly constant at 2000 m.

3.1.2. Extended Conventional P-Wave CMP Profile

The long P-wave conventional seismic CMP profile was recorded with a 0.5-ms sample rate over 264 channels, utilizing 4.5-Hz vertical geophones spaced 6.10 m apart, and had a recording time of 8 s. The source typically was 300 g (with some instances at 150 g) of explosive, placed at the bottom of a 1.5-m hole drilled in the base of the tunnel (Figure 2). The explosive was detonated via an electrical trigger controlled by the seismograph operator. Since the goal of this survey was to record higher-frequency reflected signals, a 10–500-Hz field filter was applied to reduce surface wave amplitudes. The CMP stacked section covered 1728 m, spanning a CMP elevation from 2105 m to 2111 m above mean sea level. The maximum fold of coverage was 264.

3.1.3. HVSR Sounding

We tested HVSR passive soundings at several locations using a TROMINO® three-component seismometer (0.1–1024 Hz) along the line of the long P-wave CMP profile. The seismometer was operated with a sampling rate of 128 Hz, which permitted the identification of amplification peaks up to 64 Hz (the Nyquist frequency). The instrument was oriented northward, coupled to the gravel base of the tunnel (the invert) using spikes, leveled, and set to record for 20 min.

3.2. Seismic Data Processing and Modelling Methods

3.2.1. Short Test P-Wave High-Resolution CMP Profile Processing

The data processing steps for the short test CMP profile (Figure 2) included the assignment of three-dimensional station geometry, bottom muting of near-source amplitudes to suppress surface-wave energy, Ormsby frequency bandpass filtering (20–35–200–400 Hz, trapezoidal), automatic gain control (AGC) (500-ms operator length), CMP sorting, and CMP stretch mute (attenuation of any sample moved in time by 50% or more) to remove first breaks (direct and head waves). Additionally, normal move-out (NMO) velocity analysis was performed for CMP stacking and for time-to-depth conversion, followed by the stacking of CMP-sorted traces and depth conversion. Parameters for these processes were tested to optimise the potential for shallow targets (e.g., less than 100 m depth). For instance, a range of NMO velocities was used to flatten hyperbolic arrivals, while various corner frequencies were tested for the Ormsby bandpass filter. We started applying a narrower filter by selecting the lower corner frequencies to be 35 and 60 Hz, which reduced the bandwidth and consequently the definition. Expanding the filter by substituting these values with 20 and 35 Hz, respectively, improved the definition of the final image. The application of AGC remained insensitive to operator length, as long as it exceeded the travel time of the deepest target, approximately 100 m. Deconvolution filtering was tested but was found to be destructive. Multiple reflected arrivals were not apparent in the shot records or on the CMP stack section. Post-stack migration was applied to position amplitudes and collapse diffractions accurately. Further details on seismic CMP data processing techniques can be found in [26,27,28].

3.2.2. MASW S-Wave Velocity Profile Modelling

As part of the MASW, dispersion spectra depicting phase velocity as a function of frequency [29] were computed with ParkSEIS™ [30] for the active source records and combined using a CMP roll-along technique [31,32,33]. For the reconstructed CMP MASW profile (Figure 2), we chose an optimised source-receiver offset of 18.3 m, equivalent to six times the 3.05-m receiver interval. The reconstructed CMP profile generated 72 shot records, each providing a phase-velocity vs. frequency dispersion spectrum. The spectra show a well-defined dispersion relationship within the 20 to 150 Hz frequency range, interpreted to express fundamental-mode Rayleigh waves.

3.2.3. Extended Conventional P-Wave CMP Profile Processing

Data processing for the extended P-wave CMP profile involved a comprehensive series of steps to maximise the imaging of reflectors in a difficult environment. In addition to the processing applied for the short test CMP profile, refraction statics correction, deconvolution, spectral balancing, and noise attenuation processing steps (see [27] for further explanation) proved particularly useful. Refraction statics corrections were applied in the receiver and source domains, as shown in Figure 5a. The static solution was based on a two-layer velocity-depth model (upper layer over an infinite half-space) with an elevation datum of 2200 m above mean sea level (Figure 5b). Significant static delay times were derived, reaching about 35 ms, resulting in static shifts between 0 and 24 ms (Figure 5a). Examples of common-source records before and after applying refraction statics are shown in Figure 6. Surface-consistent spiking deconvolution (which whitens the frequency spectrum) was tested in the common-source and CMP stacked domains (Figure 7a,b and Figure 8, respectively). An operator length of 160 ms with 0.1% pre-whitening produced optimal results (Figure 7a and Figure 8). Bandpass frequency filter tests were subsequently performed in the common-source (Figure 8) and CMP stacked domains (Figure 9), with the best result being 10–15–130–135 Hz (Ormsby bandpass). We then tested a progression of pre-stack surface-wave noise attenuation steps (Figure 7d). This step transforms the records from the time-space to the frequency-space domain, where it performs a frequency-dependent mix of adjacent traces to suppress low-apparent velocity noise from surface waves. The final step was time-to-depth conversion using the root-mean-square (RMS) velocity from NMO analysis. We tested post-stack time migration but found the results unhelpful due to low dip angles (<12°) for reflections and very little diffracted energy.
We experimented with reflection strength and trace (i) seismic attributes on the equivalent travel time section to independently characterise the reflectivity on the depth-converted CMP section. Reflection strength responds to variations in lithology and porosity (variations in acoustic impedance) [34,35]. Since we computed this attribute after applying gain balancing, the resulting section depicts relative changes in strength rather than absolute values (i.e., it tracks lateral variability in reflectivity). The trace (i) scalar attribute raises the trace (i) to the power of the scalar (in this case, scalar = 2), while retaining the sign of the input trace sample. This attribute displays only the most coherent events, thereby reducing the possibility of noise interference.

3.2.4. HVSR Transformation

The HVSR method provides the resonant (fundamental) frequency of the medium beneath the instrument [36,37]. This method can model the thickness of shallow subsurface bedrock and the overlying soil or gravel with S-wave velocity variation [38,39,40]. For this study, we transformed [41,42] the three-component seismic recordings into the horizontal versus vertical amplification ratio as a function of frequency, using the GRILLA™ modelling software [43]. The thickness of the layer above the bedrock can be estimated from the fundamental mode equation [41] and the S-wave velocity that was modelled from the MASW.

4. Results

4.1. Short Test P-Wave High-Resolution CMP Profile

The high-resolution CMP profile is presented as a colour raster image, unmigrated in Figure 10a. The minimum vertical resolution, estimated using the Rayleigh criterion, is 6.9 m, and the detection limit is 3.4 m (using a P-wave velocity of 4000 m/s, derived from RMS velocities, and a dominant frequency of 145 Hz, based on computing amplitude-frequency spectra on the stacked time CMP sections). Time-depth conversion utilised an average velocity of 4000 m/s, based on the RMS stacking velocity. Migration was executed with a slightly reduced velocity of 3500 m/s. The unmigrated profile displays several curved events interpreted as edge diffractions (arrows, Figure 10a) with a positive polarity that collapse into flat segments upon migration (arrows, Figure 10b). The profile was situated over two intersecting faults, previously mapped with the tunnel. Plotting the locations of these faults where they are believed to intersect the invert allows for an interpretation of the shallow subsurface based on the termination of horizontal reflectors and the associated edge diffractions (Figure 10a). During the survey, we monitored the field records for interference from small side galleries occasionally intersecting the main adit. No interference was noted, and the processed CMP stacked sections do not exhibit any such effects (e.g., out-of-plane diffraction). Based on the above calculations for vertical resolution, the dominant wavelength is estimated to be about 28 m. Given that the entrance to the side galleries is no larger than approximately 3 × 3 m (i.e., small compared to the dominant wavelength), we would not anticipate any significant interference.

4.2. MASW S-Wave Velocity Profile

Phase velocity as a function of frequency spectra, as shown in Figure 11, was inverted, and the S-wave velocity models were interpolated into a colour-raster cross-section down to a depth of 40 m (Figure 12). In the southeastern part of the profile, the shear-wave velocity inverse modelling indicates a complex velocity range of about 2400 m/s just beneath the base of the invert, reaching as much as 3600 m/s, including velocity inversions. The northwestern part of the cross-section (Figure 12) shows a different, albeit simpler, result—velocities as low as about 1000 m/s and exceeding 3000 m/s. We interpret a fault based on the lateral change in the velocity pattern illustrated in Figure 12.

4.3. Extended Conventional P-Wave CMP Profile

In keeping with the experimental focus of this study, we present the results of the extended P-wave CMP stacked section in various modes: as unmigrated amplitude as a function of depth (Figure 13a), as a wiggle-trace variable area section (Figure 13b), as a trace (i) Scalar attribute section (Figure 13c), and with the reflection strength attribute (Figure 13d). The depth-converted sections are displayed down to 2000 m, below which we do not interpret primary reflectivity. The equivalent lower limit on the travel time sections is about 800 ms (i.e., an average P-wave velocity of 5000 m/s). Vertical resolution is 24 m, and the detection limit is 12 m (using a maximum P-wave velocity of 5000 m/s, derived from RMS velocities, and a dominant frequency of 52 Hz, based on computing amplitude-frequency spectra on the stacked time CMP sections).
The uppermost part of the unmigrated CMP amplitude depth section (0–150 or 200 m below datum) (Figure 13a) is characterised by short reflector segments (no longer than a few hundred meters) that correspond to brief hyperbolic reflections on shot records in the upper 50–75 ms (Figure 7a). Some segments are less than 100 m and more discontinuous. The overall package deepens from 175 m at the eastern edge of the section to 210 m at the western edge, dipping to the west. Below 200 m, the depth section (Figure 13b) becomes less reflective, featuring sub-horizontal and gently dipping reflectors, typically 50–250 m in length. This behaviour is illustrated by the reflection strength attribute (Figure 13d). The trace (i) Scalar attribute section (Figure 13c) reduces incoherent noise while enhancing the visibility of individual reflectors and reflector segments. Both east- and west-dipping reflectors are visible in the plane of the section (Figure 13c), although most dip to the west. Dipping reflectors exhibit an unmigrated apparent dip of 8–12° west, which, according to the straight-ray migration equation [26], corresponds to a dip of 8.1–12.3°.
We tentatively interpret the shallow reflectivity (50–150 m) as gently northwest-dipping stratigraphy in the Permian Queantoweap Sandstone and the underlying Pennsylvanian Callville Limestone. The shallowest part of this primary reflectivity (0–50 m) is represented as reflectors on the short test high-resolution P-wave CMP profile (Figure 10) and as S-wave velocity contrasts on the test MASW profile (Figure 11). However, it is possible that some events could be incompletely filtered or muted surface-wave energy. According to the geological cross-section along the PTH tunnel in [21,22], the contact between the Permian Queantoweap Sandstone and the underlying Pennsylvanian Callville Limestone beneath the tunnel at about 250 m is approximately 12 degrees to the northwest, which roughly matches the dip of deeper reflectors on the CMP depth section (Figure 13c).

4.4. HVSR Soundings

The underground HVSR results varied in quality, possibly due to noise contamination from machinery operating in the mine (electrical generators and ventilation). For transformation, we selected two of the highest quality spectra (Figure 14) near the two short test seismic profiles (Figure 2). These display a narrow peak between 12 and 14 Hz, which we interpret as representing the base of the tunnel invert (Figure 3). The lower part of the spectra shows a prominent peak between 4 and 6 Hz (Figure 3). Using an average upper-layer S-wave velocity of 2000 m/s (Figure 12), the fundamental mode equation yields 114 m and 94 m upper-layer thicknesses for stations 163 and 213, respectively. We interpret the results as indicating a transition to a higher S-wave velocity, approximately corresponding to the base of the shallow reflectivity on the extended CMP seismic profile (Figure 13d).

5. Discussion

The experimental deployment of four different seismic exploration methods in the historic Deer Trail metals mine demonstrates their potential for detecting stratigraphic boundaries and tectonic structures in terms of primary reflectivity, as well as S-wave velocity contrasts. The various methods represent subsurface geology from different perspectives and with varying limitations. The short test P-wave high-resolution CMP survey, utilizing an accelerated elastic weight-dropper source with finer station spacing, successfully detected shallow reflectors and structural reflector truncations associated with intersecting faults to a depth of about 140 m. By repurposing the same receiver array, we employed Rayleigh-wave dispersion to invert the shallow (<40 m) S-wave velocity structure, which reveals evidence of fault offsets and velocity inversions.
The extended conventional P-wave CMP survey utilised an explosive source, enabling greater reflector imaging depth penetration. Simultaneously, the coarser station interval reduced spatial sampling compared to the high-resolution test CMP profile. The extended conventional P-wave CMP section underwent a more sophisticated processing stream to enhance the chances of detecting deep reflectors. Discontinuous sub-horizontal and dipping reflectors, along with reflector segments, were imaged deep in the section, interpretable as stemming from bedding-related acoustic impedance contrasts in bedrock, possibly indicating shaly zones within a more pervasive sandstone or limestone medium. It is also possible that some reflectivity represents discontinuous mantos-style ore bodies located in limestone country rock. Conversely, the extended CMP survey did not detect tectonic structures, potentially due to insufficient seismic impedance contrasts in a narrow deformation zone or a lack of well-defined stratigraphic offsets.
For both the experimental P-wave CMP reflection and the extended P-wave CMP reflection profiles, the active-source energy propagated the full length of the receiver arrays: 290 m and 1603 m, respectively. Highly distorted first-break arrival times necessitated source and receiver-based refraction-static modelling as a critical processing step. Rayleigh-wave energy was moderately intense, benefiting the MASW generation of an S-wave velocity model; however, this energy interfered with the weaker reflections and required an apparent velocity-based noise suppression step.
The HVSR results are valuable for constraining the depth to harder (i.e., higher S-wave velocity) layers, which, in this case, approximately correlate with the base of shallow reflectivity. The resonant frequency for the hard recrystallised bedrock beneath the invert ranged between 4 and 10 Hz, consistent with previous studies of non-sedimentary bedrock [42] and well below the Nyquist frequency of 64 Hz associated with our sample rate. Higher sample rates would not have resolved additional velocity structures in the bedrock.
Among the challenges for seismic imaging are the economic targets that involve fault surfaces or shear zones, reactive clean limestone intervals, and shale layers within the limestone. The thickness and lateral extent of such targets may be small relative to the seismic wavelengths that remain at depth with absorptive country rock. Pervasive recrystallization and fracturing of limestones and clastic sedimentary rocks, as directly observed in the tunnel, could reduce the acoustic impedance contrasts necessary to produce significant reflectivity. Integrating several seismic methods enhances our understanding of the potential for detecting structure and stratigraphy from surveys conducted in an environment that is challenging for deployment, recording, and imaging.
Future experimental work could involve placing seismic sources and receivers on or within tunnel walls to create a three-dimensional image [44,45]. When applied to the 100-year-old Deer Trail Mine, this method could reveal old, unmapped mining galleries or tunnels, the existence of which could pose hazards for further resource extraction.

6. Conclusions

  • The four methods complement each other in terms of resolution, depth penetration, and responsiveness to the elastic parameters of geological targets.
  • The short test P-wave CMP profile resolves finer details (e.g., diffractors; small stratal offsets), but it has limited depth penetration compared to the extended P-wave CMP profile, which offers a vertical resolution and depth limit closer to petroleum industry surveys [26,27].
  • On the other hand, the MASW S-wave velocity profile responds only to variations in shear modulus rather than to discrete changes (i.e., reflectors) in both bulk and shear modulus [28,29].
  • The HVSR method provides the lowest resolution (i.e., lowest frequency, less than 10 Hz) but can detect fundamental subsurface boundaries with S-wave variations; furthermore, it is the easiest survey by far.

Author Contributions

Conceptualization, R.W.K., J.H.M. and L.L.; methodology, J.H.M., K.A.R. and S.T.N.; software, J.H.M. and S.T.N.; formal analysis, J.H.M. and S.T.N.; investigation, J.H.M., L.L. and R.W.K.; data curation, K.A.R.; writing—original draft preparation, J.H.M.; writing—review and editing, J.H.M., L.L. and S.T.N.; visualization, J.H.M.; supervision, L.L.; project administration, L.L.; funding acquisition, L.L. and J.H.M. All authors have read and agreed to the published version of the manuscript.

Funding

Principal funding for this project came from DT Mining 100% subsidiary of MAG Silver Corp. Partial funding was also provided by the College of Physical and Mathematical Sciences at Brigham Young University. A generous software grant from the Landmark (Halliburton) University Grant Program supported the seismic data processing and analysis.

Data Availability Statement

The datasets presented in this article are not readily available because the data are part of an ongoing study.

Conflicts of Interest

Author Stephen T. Nelson was employed by the company MAG Silver. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Figure 1. General location map of the conterminous USA featuring the physiographic shaded relief map of the State of Utah. The location of the DT Mine is indicated. Quaternary faults and folds [19] are displayed in black.
Figure 1. General location map of the conterminous USA featuring the physiographic shaded relief map of the State of Utah. The location of the DT Mine is indicated. Quaternary faults and folds [19] are displayed in black.
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Figure 2. (a) Geologic map, blended with shaded relief, of the study area. Stratigraphic symbols are Qaf1: Young alluvial-fan deposits (Holocene); Qms: Landslide deposits (Holocene and upper Pleistocene); Qaf3: Middle alluvial-fan deposits (middle Pleistocene); Jn: Navajo Sandstone (lower Miocene); TRc: Chinle Formation (Upper Triassic); TRm: Moenkopi Formation (Lower Triassic); Pkt: Kaibab and Toroweap Formations, undivided (upper Permian). Source: [24]. The projection of the PTH Tunnel to the ground surface is shown. (b) An inset map shows the location of the three seismic profiles as coloured lines. The numbers 163 and 213 refer to the locations of the two HVSR soundings discussed in the text.
Figure 2. (a) Geologic map, blended with shaded relief, of the study area. Stratigraphic symbols are Qaf1: Young alluvial-fan deposits (Holocene); Qms: Landslide deposits (Holocene and upper Pleistocene); Qaf3: Middle alluvial-fan deposits (middle Pleistocene); Jn: Navajo Sandstone (lower Miocene); TRc: Chinle Formation (Upper Triassic); TRm: Moenkopi Formation (Lower Triassic); Pkt: Kaibab and Toroweap Formations, undivided (upper Permian). Source: [24]. The projection of the PTH Tunnel to the ground surface is shown. (b) An inset map shows the location of the three seismic profiles as coloured lines. The numbers 163 and 213 refer to the locations of the two HVSR soundings discussed in the text.
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Figure 3. (a) Photograph inside the PTH tunnel showing bedrock character of the tunnel, old narrow-gauge rail, and deployment of seismic recording equipment. (b) Photograph in tunnel showing deployment of three-component seismometer. Photograph by J. McBride.
Figure 3. (a) Photograph inside the PTH tunnel showing bedrock character of the tunnel, old narrow-gauge rail, and deployment of seismic recording equipment. (b) Photograph in tunnel showing deployment of three-component seismometer. Photograph by J. McBride.
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Figure 4. Accelerated elastic weight dropper (45-kg) used for short test CMP and MASW seismic profile in the PTH tunnel, view looking southeast. Photograph by J. McBride.
Figure 4. Accelerated elastic weight dropper (45-kg) used for short test CMP and MASW seismic profile in the PTH tunnel, view looking southeast. Photograph by J. McBride.
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Figure 5. (a) Summary of refraction statics data processing results derived along the extended CMP seismic profile. Red dots represent source static time delays, while blue dots indicate receiver static time delays. (b) Velocity-depth solution obtained from the static delays and refractor velocity for a classic two-layer solution, with the lower layer being an infinite half-space.
Figure 5. (a) Summary of refraction statics data processing results derived along the extended CMP seismic profile. Red dots represent source static time delays, while blue dots indicate receiver static time delays. (b) Velocity-depth solution obtained from the static delays and refractor velocity for a classic two-layer solution, with the lower layer being an infinite half-space.
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Figure 6. (Top): Example of two raw common-source records from near the beginning of the extended conventional production seismic CMP profile. Note the distortion of the arrival time of the critically refracted arrival (“headwave”). (Bottom): The same two records with the refraction static solution (Figure 5) applied. Arrows indicate where the static solution had a significant impact.
Figure 6. (Top): Example of two raw common-source records from near the beginning of the extended conventional production seismic CMP profile. Note the distortion of the arrival time of the critically refracted arrival (“headwave”). (Bottom): The same two records with the refraction static solution (Figure 5) applied. Arrows indicate where the static solution had a significant impact.
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Figure 7. (a) Four non-consecutive common-source records with normal move-out (NMO) applied based on stacking velocity analysis, including a top muting function (to remove direct and head waves), as shown, but without bandpass frequency filtering and spiking deconvolution. (b) The same as above, but with spiking deconvolution applied. (c) The same as above, but with an Ormsby bandpass frequency filter (10–15–130–135 Hz). (d) The same as above, but with surface-wave noise attenuation applied. The reflection fields, surface-wave zones, and areas of CMP stretch are noted.
Figure 7. (a) Four non-consecutive common-source records with normal move-out (NMO) applied based on stacking velocity analysis, including a top muting function (to remove direct and head waves), as shown, but without bandpass frequency filtering and spiking deconvolution. (b) The same as above, but with spiking deconvolution applied. (c) The same as above, but with an Ormsby bandpass frequency filter (10–15–130–135 Hz). (d) The same as above, but with surface-wave noise attenuation applied. The reflection fields, surface-wave zones, and areas of CMP stretch are noted.
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Figure 8. (a): First 500 ms of the brute CMP stack travel time section of the extended conventional production profile without spiking deconvolution. (b): The same as above, but with spiking deconvolution applied (see text for further explanation).
Figure 8. (a): First 500 ms of the brute CMP stack travel time section of the extended conventional production profile without spiking deconvolution. (b): The same as above, but with spiking deconvolution applied (see text for further explanation).
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Figure 9. Testing bandpass frequency filters on the final part of the brute stack from the extended conventional seismic CMP travel time brute stack, which includes automatic gain control (500-ms window). The optimal composite frequency filter is determined to be 10–15–130–135 Hz.
Figure 9. Testing bandpass frequency filters on the final part of the brute stack from the extended conventional seismic CMP travel time brute stack, which includes automatic gain control (500-ms window). The optimal composite frequency filter is determined to be 10–15–130–135 Hz.
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Figure 10. (a) High-resolution P-wave seismic CMP profile (Figure 2), unmigrated. Dashed lines indicate interpreted faults as intersected in the adit. Vertical arrows mark the interpreted apices of diffractions. The elevation datum is 2000 m above mean sea level. (b) Same as above, migrated.
Figure 10. (a) High-resolution P-wave seismic CMP profile (Figure 2), unmigrated. Dashed lines indicate interpreted faults as intersected in the adit. Vertical arrows mark the interpreted apices of diffractions. The elevation datum is 2000 m above mean sea level. (b) Same as above, migrated.
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Figure 11. The demonstration of phase velocity as a function of frequency illustrates surface-wave dispersion used for the inverse modelling depicted in Figure 12. The white dashed line is the interpreted dispersion function.
Figure 11. The demonstration of phase velocity as a function of frequency illustrates surface-wave dispersion used for the inverse modelling depicted in Figure 12. The white dashed line is the interpreted dispersion function.
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Figure 12. Shear-wave velocity depth model resulting from the modelling of surface-wave dispersion spectra, as shown in Figure 11. The portion of the cross-section without CMP coverage is omitted. The dashed line indicates an interpreted fault or discontinuity.
Figure 12. Shear-wave velocity depth model resulting from the modelling of surface-wave dispersion spectra, as shown in Figure 11. The portion of the cross-section without CMP coverage is omitted. The dashed line indicates an interpreted fault or discontinuity.
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Figure 13. Final seismic CMP stacked depth section for the extended profile: (a) displayed as a colour raster, (b) wiggle-trace variable area section (trace bias = −25%; trace excursion = 2.3), (c) trace (i) Scalar where Scalar = 2, with interpreted reflectors (diffractor noted by vertical arrow), and (d) the same section above, but processed as a reflection strength attribute.
Figure 13. Final seismic CMP stacked depth section for the extended profile: (a) displayed as a colour raster, (b) wiggle-trace variable area section (trace bias = −25%; trace excursion = 2.3), (c) trace (i) Scalar where Scalar = 2, with interpreted reflectors (diffractor noted by vertical arrow), and (d) the same section above, but processed as a reflection strength attribute.
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Figure 14. Top: Horizontal/vertical amplification ratio (H/V) from the HVSR soundings using a low-frequency three-component seismometer at station 163, located near the high-resolution P-wave CMP profile (Figure 2b). Bottom: as above, but for station 213, which is situated further northwest of the CMP profile (Figure 2b). Note the narrow peaks centred between 12 and 14 Hz, interpreted as the loose gravel and weathered rock directly below the invert.
Figure 14. Top: Horizontal/vertical amplification ratio (H/V) from the HVSR soundings using a low-frequency three-component seismometer at station 163, located near the high-resolution P-wave CMP profile (Figure 2b). Bottom: as above, but for station 213, which is situated further northwest of the CMP profile (Figure 2b). Note the narrow peaks centred between 12 and 14 Hz, interpreted as the loose gravel and weathered rock directly below the invert.
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MDPI and ACS Style

McBride, J.H.; Lambeck, L.; Rey, K.A.; Nelson, S.T.; Keach, R.W. Experimental Seismic Surveying in a Historic Underground Metals Mine. Geosciences 2025, 15, 221. https://doi.org/10.3390/geosciences15060221

AMA Style

McBride JH, Lambeck L, Rey KA, Nelson ST, Keach RW. Experimental Seismic Surveying in a Historic Underground Metals Mine. Geosciences. 2025; 15(6):221. https://doi.org/10.3390/geosciences15060221

Chicago/Turabian Style

McBride, John H., Lex Lambeck, Kevin A. Rey, Stephen T. Nelson, and R. William Keach. 2025. "Experimental Seismic Surveying in a Historic Underground Metals Mine" Geosciences 15, no. 6: 221. https://doi.org/10.3390/geosciences15060221

APA Style

McBride, J. H., Lambeck, L., Rey, K. A., Nelson, S. T., & Keach, R. W. (2025). Experimental Seismic Surveying in a Historic Underground Metals Mine. Geosciences, 15(6), 221. https://doi.org/10.3390/geosciences15060221

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