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Near-surface Seismic Investigation of Barringer (Meteor) Crater, Arizona

Soumya Roy1 and Robert R. Stewart1

1Department of Earth and Atmospheric Sciences,

Email: [email protected] of Houston, Houston, TX 77204

Near-surface Seismic Investigation of Barringer (Meteor) Crater, Arizona

Soumya Roy1 and Robert R. Stewart1

1Department of Earth and Atmospheric Sciences, University of Houston, Houston, TX 77204

Email: [email protected]

ABSTRACT

We investigated the shallow subsurface of Barringer (Meteor) Crater, Arizona using high-resolution seismic methods. The seismic surveys were conducted in May, 2010 during a joint

expedition by the University of Houston, the University of Texas at Austin, and the Lunar and

Planetary Institute (LPI). We performed compressional (P)-wave refraction analysis on the

seismic data and found P-wave velocities of 450–2,500 m/s for a 55-m deep model. Away from

the crater rim (toward the south), the shallow P-wave low-velocity layers thin. We also estimated a

near-surface, shear (S)-wave velocity structure using a surface-wave inversion method. S-wave

velocities vary from 200–700 m/s for the top 16–20 m, increasing to 900–1,000 m/s at 38-m depth.

We interpret a prominent change in S-wave velocity (at around 500–600 m/s) as the transitionfrom the ejecta blanket (a sheet of debris thrown out of the crater during the impact) to the bed-

rock Moenkopi sandstone. The ejecta is characterized as unconsolidated, low velocity, and low

density. This S-wave transition takes place at a depth range of 12–20 m near the crater rim with a

thinning away from the crater rim. This consistent P-wave and S-wave structure is interpreted as

the ejecta blanket. Ultrasonic measurements on hand samples collected during the expedition give

a range of P-wave velocities of 800–1,600 m/s for the Moenkopi. Predicted bulk densities from

estimated S-wave velocities using modified Gardner’s equation fall in the range of 1.8–2.5 gm/cm3,

with low-density materials (ejecta) underlain by high-density materials (bedrock). These densityresults, along with available drilling information and residual gravity anomalies, also support the

thinning of the ejecta blanket.

Introduction

Barringer (Meteor) Crater, situated near Winslow,

Arizona, was excavated some 49,000 years ago by the

collision of a high-velocity iron-nickel meteorite with the

Colorado Plateau. The impact energy was equivalent to

10 MT of TNT, creating a crater with a diameter of

approximately 1.2 km (Kring, 2007). The crater rim rises

some 30–60 m above the surrounding plain and encircles

an approximately 180-m deep bowl-shaped depression.

The near-surface of the crater is fractured, brecciated,

and unconsolidated, having mixed debris of different

strata and meteoritic materials. A number of questions

remain unanswered about this impact structure includ-

ing its asymmetry, depths and orientation of fractures,

thickness of ejecta blanket (the layer of debris thrown

out of the crater during the impact), and rock pro-

perties. We undertook a suite of geophysical measure-

ments in May, 2010 to attempt to answer some of these

questions. The University of Houston, the University

of Texas (Austin), and the Lunar and Planetary Ins-

titute (LPI) led a joint geophysical expedition at the

crater site. In this paper, we present seismic, ultrasonic

and gravity results. The primary goals of this work are

to: a) obtain the near-surface seismic velocity structure,

and b) estimate the ejecta blanket thickness. In addi-

tion, this study also addresses some broader seismic

and planetary surface issues as: a) whether seismic

waves can propagate through brecciated materials, b)

the development of general survey methodologies to

determine ejecta thicknesses in various craters, c) how

to image near-surface faults associated with the impact

mechanism, and d) where to drill for rock physics

purposes.

Geological Setting of Barringer Crater

Barringer (Meteor) Crater is categorized as a

simple crater (a small impact structure with a relatively

smooth bowl-shaped depression, no central uplift, and

the depth of the crater much less than the diameter).

Figure 1(a) shows a schematic diagram of the final stage

of a simple crater. The present day stratigraphy (a

normal upper Grand Canyon sequence) near the Meteor

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JEEG, September 2012, Volume 17, Issue 3, pp. 117–127

crater consists of white Coconino sandstone overlain

by the very thin Toroweap sandstone, followed by the

yellowish Kaibab dolomite and minor sandstone, and

then the red Moenkopi siltstone at the top. The impact

created an inverted or overturned stratigraphy so that

the layers immediately exterior to the rim are stacked

in the opposite order in which they normally occur.

The overturned layers (‘‘ejecta blanket’’) extend to a

distance of one to two kilometers outward from the

crater’s edge. Thus, the entire sequence around the

crater from the top to bottom is the ejecta blanket

(debris from Coconino-Kaibab-Moenkopi) underlain

by the bedrock Moenkopi-Kaibab-Coconino (Fig.1(b)).

The ejecta blanket also contains other materials (e.g.,

fragments of meteorites, recent alluvium) mixed with the

excavated debris (Kring, 2007).

Physical Properties of the Geological Units

Early studies (Walters, 1966; Watkins and Wal-

ters, 1966; Ackermann et al., 1975) characterized some

of the physical properties of the Barringer Crater units.

The near-surface of the crater is unconsolidated, dry

with a low bulk density. Hence, a low near-surface

velocity is also expected. A summary of the average

thicknesses and range of the bulk densities for different

near-surface units obtained from previous work and

drilling results is provided in Table 1.

Bulk densities are often predicted from P-wave

velocities (VP), using Gardner’s relationship (Gardner

et al., 1974). We predicted average bulk densities from VP

(obtained from ultrasonic transmission measurements

during the expedition) using Gardner’s relationship r 5

0.23 VP0.25, where r is the bulk density in gm/cm3 and VP

is the P-wave velocity in ft/s. Ranges of VP values from the

ultrasonic measurements are also given in Table 1 along

with predicted bulk densities. Details of the ultrasonic

transmission method and results are provided later. It is

also possible to predict bulk densities from S-wave

velocities (VS) using a modified Gardner’s relationship

(Dey and Stewart, 1997; Potter and Stewart, 1998). The

modified Gardner’s relationship for VS can be represented

as r 5 aVSb, where r is the bulk density in gm/cm3, VS is

the S-wave velocity in ft/s, a 5 0.37 and b 5 0.22 (Potter

and Stewart, 1998). The results regarding predicted

densities from VS are also discussed later in the paper.

Figure 1. (a) Schematic diagram (French, 1998; Kring, 2007) showing the final stage of a simple crater, such as

Barringer Crater, and (b) schematic diagram of the stratigraphy at Barringer Crater (modified after Shoemaker et al.,1974; Kring, 2007).

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Journal of Environmental and Engineering Geophysics

Geophysical Surveys at the Crater

We performed a set of test seismic surveys on the

southern portion of the crater (Fig. 2(a)). One set

of experiments was performed using a 4.5-kg (10-lb)

sledgehammer as the source, and another set of

experiments was performed using a 40-kg (88-lb)

accelerated weight drop (AWD). For the NW-SE

trending seismic line 1, the source was the sledgehammer

(hence, we name seismic line 1 as hammer line) and the

receivers were planted vertical geophones. The hammer

line is 66-m long (34 receiver stations with 2-m

intervals). For the N-S trending seismic line 2, the

source was a truck-mounted AWD (hence, we name

seismic line 2 as AWD line) and receivers were again

planted vertical geophones. The AWD line is 645-m long

(216 receiver stations with 3-m intervals). The starting

position of the AWD line is approximately 600-m away

from the center of the crater. All vertical geophones used

in this survey have a natural frequency of 14 Hz. A

summary of the seismic acquisition parameters is

provided in Table 2.

Gravity surveys were conducted along five differ-

ent survey lines on the southern part of the Meteor

crater. One of the main gravity lines is exactly along the

AWD seismic line. The gravity line starts closer to the

rim and overlaps with 0–570 m portion of the AWD line

(0–645 m). Gravity stations were 30-m apart. At every

station, three readings of 60-s each were recorded using

a Scintrex CG-5 gravimeter. Some initial gravity results

along the AWD seismic line are discussed here and in

Turolski (2012). In addition, we performed ultrasonic

transmission measurements (using a James Instrument

V-meter) on a number of hand specimens during the

expedition to estimate the P-wave velocities of different

lithologies.

Figure 2(b) shows an overlay map of the seismic

lines and the approximate locations of several rotary

drill-holes (marked as stars) from Roddy et al. (1975).

The ‘‘South Line’’ and the ‘‘South East Line’’ (Roddy

et al., 1975) indicated in the drill-hole location map

Figure 2. (a) Satellite image showing the location of

Barringer (Meteor) Crater and seismic lines used in this

study. (b) Overlay image of the Meteor Crater with

seismic lines and approximate locations of several drill-

holes (marked in stars) from the rotary drilling program

of Roddy et al. (1975). The drill-hole lines (‘‘South Line’’

and ‘‘South East Line’’) and available drill-holes (markedas stars with surrounding white circles) from the same

drilling program closest to the seismic lines are also

plotted (Google Earth plots).

Table 1. Summary of the ranges of average thicknesses, average P-wave velocities, and dry bulk densities of differentunits at the Barringer Crater from previous work (Walters, 1966; Watkins et al., 1966; Kring, 2007) and ultrasonic

measurements from May, 2010.

Target units

Average

thicknesses (m)

Average P-wave

velocities (m/s) from

ultrasonic measurements

Bulk densities

(gm/cm3) from

drill cores

Predicted bulk

densities (gm/cm3) from

P-wave velocities

Ejecta blanket 0–26 N/A 1.87–2.17 N/A

Moenkopi formation 12.3 800–1,600 2.19–2.48 1.65–1.96

Kaibab formation 73 2,530–3,720 2.12–2.68 2.19–2.42

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Roy and Stewart: Seismic Investigation of Barringer Crater, Arizona

(Fig. 2(b)) are the nearest drill-hole lines to our seismic

lines. We used ejecta blanket thickness results from

this drilling program to compare our results during

interpretation.

Methodology

One of the main objectives of this paper is to create

a high-resolution, near-surface velocity structure and

hence to try to identify different layers. We gave special

emphasis to estimating the S-wave velocity (Vs)

structure as no S-wave velocity structure has been

determined for the Barringer Crater. We applied the

surface-wave (Rayleigh wave or ground-roll) inversion

method to obtain the S-wave velocity structure (using

the Multichannel Analysis of Surface Waves (MASW)

method from Park et al., 1998; Park et al., 1999; Xia

et al., 1999). MASW is based on the frequency-

dependent properties of surface waves to create disper-

sion curves (phase velocity versus frequency plots). These

dispersion curves are inverted for the fundamental (and

higher) modes to obtain the near-surface Vs structure.

We undertook careful assessment of the offset and

spread lengths used in our multi-mode MASW inversion

(Park et al., 2001; Park and Ryden, 2007; Park, 2011).

The higher modes have greater velocities than the

fundamental mode at a particular frequency; hence,

they have longer wavelengths and can penetrate deeper.

Using higher modes may provide improvement in

velocity estimations (Wisen et al., 2010).

We also used a P-wave refraction analysis method.

In this method, we first pick the first-break arrival times

of the raw shot gathers, generate an initial VP model,

and then an iterative travel-time tomography is per-

formed. In the tomographic technique, rays are traced

through an iteratively updated velocity model with the

goal of minimizing the difference between calculated

and observed travel times. This procedure produces the

final VP structure. We used the Geometrics SeisImager

refraction software for this purpose.

Results

During the expedition, P-wave velocities for

Moenkopi and Kaibab hand samples were measured

on the interior slopes of the northern rim of Meteor

Crater using ultrasonic transmissions with the field

portable V-meter (Table 3). Rock types were identified

by D. Kring (LPI). Measured VP values are in the range

of 815–1,570 m/s (measuring errors varying from 4–9%)

for Moenkopi samples and 2,560–3,705 m/s (measuring

errors varying from 2–9%) for Kaibab samples. The

probable reasons of the variations in VP values are: 1)

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of very irregular shapes and sizes, and 3) measurement

errors. Nevertheless, the values give a general idea of the

P-wave velocities of the different lithologies at the crater

and help to understand the seismic results.

We then performed a detailed study of the seismic

raw shot gathers. Shot gathers from different seismic

lines are shown in Fig. 3. Figure 4 shows a series of

amplitude spectra for different raw shot gathers from

hammer and AWD lines. Hammer-seismic data show

the dominance of higher frequencies (around 100 Hz)

compared to AWD data (around 50 Hz) for a near-

offset range. However, for the middle to far offsets, the

amplitude spectra share a comparable range of frequen-

cies for both hammer and AWD lines. For the AWD

case, the weight of the source is greater and produces

more energy. This increase in energy is observed in the

amplitude spectra (Fig. 4) as AWD data show higher

true amplitude values.

Next, we undertook P-wave refraction analysis for

the 645-m long AWD line. We used a minimum VP of

450 m/s and maximum of 3,000 m/s for a 55-m deep

model for the travel-time tomography. The minimum

and maximum VP values are based on the initial analysis

of first-break picks for several raw shot gathers alongwith ultrasonic results. We find a final P-wave velocity

model with a range of VP values varying from 450 m/s to

2,500 m/s up to 55-m depth (Fig. 5).

Surface-wave inversion (MASW) was next applied

to estimate the S-wave velocities. We used the SurfSeis

3.0 (Kansas Geological Survey) software package.

Careful selections of offset ranges have been made to

avoid (as much as possible) the mixing of differentmodes. For the hammer line, the most useful offset

range from the source is 9–55 m, whereas the offset

range is longer (10.5–82.5 m) for the AWD line. The

dispersion curves from single raw shot gathers for

selected offset ranges are shown in Fig. 6. The AWD

line is richer in lower frequencies than the hammer line

(Fig. 4), and thus provides more robust low-frequency

velocity information (Fig. 6).

The final step in the surface-wave inversionmethod is to invert the dispersion curves using

fundamental (and higher modes) for S-wave velocity.

The inversion of one dispersion curve corresponding

to one shot gather produces a 1-D S-wave velocity

structure at the center of the selected offset spread.

Multiple 1-D velocity profiles along a seismic line are

then merged into a 2-D velocity profile. Such 2-D S-

wave velocity profiles for the hammer and the AWD lineare shown in Fig. 7. The VS structure from the hammer

line (Fig. 7(a)) shows a range of velocities from 200–

700 m/s up to 16.5-m depth and increases to 1,000–

1,200 m/s below that. The 2-D S-wave velocity

structure for the AWD line shows a range of velocities

from 300–1,000 m/s up to 38-m depth and increases to

1,200–1,300 m/s below that (Fig. 7(b)). S-wave veloc-

ities increase away from the crater rim, as with the P-wave results. The deeper velocity structures from the

AWD line, compared to the hammer-seismic line, are

Table 3. Ultrasonic measurements of Moenkopi and Kaibab hand specimens showing approximate ranges of P-wave velocities.

Rock formation Thickness (mm) Transit time (ms) P-wave velocity (m/s)

Moenkopi 1 41.42 6 1.0 50.8 6 0.8 815 6 33

Moenkopi 2 32.40 6 1.0 25.82 6 1.4 1,255 6 106

Moenkopi 3 34.03 6 1.0 21.675 6 0.6 1,570 6 89

Kaibab 1 68.65 6 1.0 18.53 6 0.15 3,705 6 81

Kaibab 2 32.44 6 1.0 12.675 6 0.65 2,560 6 210

Figure 3. (a) A raw shot gather from seismic line 1

(hammer line), and (b) a raw shot gather from seismic line

2 (AWD line) at Barringer Crater, Arizona (AGCapplied). The trends of first break picks are shown by

solid lines.

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Figure 4. (a)-(c) Amplitude spectra with true amplitude values for seismic line 1 (hammer line) and seismic line 2 (AWD

line) for different source-receiver offset ranges.

122


obtainable because of more deeply penetrating and

propagating source energy.

Interpretation

In this section, we interpret the velocity models to

identify different stratigraphic layers and ejecta blanket

thickness. Previous work identified the transition from

the ejecta blanket to the Moenkopi based on changes in

P-wave velocities from refraction surveys and changes

in physical properties from drill cores (bulk density,

Young’s and Shear modulus).We compare our estimates

with one seismic refraction survey (Ackermann et al.,

1975) and several drill core results (Watkins and

Walters, 1966; Roddy et al., 1975).

Ackermann et al. (1975) showed a low-velocity

layer of 500–750 m/s for the top 15 m (roughly

consistent with the ejecta blanket thickness) followed

by an intermediate velocity zone of 750–1,500 m/s from

P-wave refraction analysis. They suggested all velocities

less than 1,500 m/s indicate unconsolidated, fractured

materials. We estimated P-wave velocities of 450–2,500 m/

s for up to 55-m depth with low-velocity layers tapering

away as we move southward. We interpret this as

the thinning of the low-velocity, unconsolidated ejecta

blanket away from the crater rim. We also obtained P-

wave velocities of 800–1,600 m/s for the Moenkopi hand

specimens from ultrasonic measurements during the

expedition. These values are in the neighborhood of

the Ackermann et al. (1975) and our P-wave refraction

results.

In addition to interpreting P-wave velocities, we

also estimated the ejecta blanket thickness from S-wave

velocities (the first attempt to do so to our knowledge at

Barringer Crater) along with the prediction of bulk

densities. We identified prominent S-wave velocity

changes (at around 500–600 m/s) at depths varying

from 15–20 m near the crater rim (up to 800–900 m from

the center of the crater, i.e., 200–300 m from the

beginning of the AWD line) on the southern flank. We

interpret this change as the transition from the ejecta

blanket to Moenkopi. As we move further away from

the crater rim, similar to the P-wave results the VS

values also increase. A summary of the depths of

transition from the ejecta blanket to the Moenkopi

obtained from previous studies are provided in Table 4,

along with the results obtained from the surface-wave

inversion method.

We also predicted bulk densities from VS (using

modified Gardner’s relation), which are in the range of

1.8–2.5 gm/cm3 (Fig. 8(a)). Closer to the crater rim,

a transition from lower densities (ejecta) to higher

densities (bed-rock) is calculated at depths varying from

15–20 m. Densities increase at around 800–900 m

distance from the crater center, indicating the consoli-

dation of materials and thinning of low-density ejecta

materials. These predicted bulk densities are in the range

of density values from previous drilling results (Tables 1

and 5) and consistent with seismic results.

The residual gravity anomaly results along the

AWD line from Turolski (2012) show a low in the

gravity field near the rim, then a rise (at around 800–

900 m from the center of crater) followed by another

decrease at the end (Fig. 8(b)). The initial decrease

probably indicates low-density unconsolidated materials

(ejecta blanket), followed by an increase in densities.

This is consistent with our predicted density results.

Turolski (2012) interpreted the gravity field decrease at

the end of the line as an effect of dipping beds.

We also received LiDAR (Light detection and

ranging) data to better estimate the crater’s topography.

The airborne LiDAR data were acquired by the National

Center for Airborne Laser Mapping (NCALM). The

resulting topographic maps have a horizontal resolution

of 25 cm and a vertical resolution of 5 cm. The last 100 m

of the AWD line do not overlap the LiDAR data,

therefore they were extrapolated using a second-order

polynomial fit (Turolski, 2012). The P- and S-wave

velocity models are re-plotted along with actual eleva-

tions. The P- and S-wave velocity models along with

elevations and distances from the center of the crater are

shown in Figs. 9(a) and 9(b). The probable transition

from the ejecta blanket to Moenkopi is also marked

(dotted black line). Figure 9(c) shows a composite plot of

the transition depths from: 1) the ‘‘South Line’’ (Roddy

Figure 5. A 2-D P-wave velocity model estimated usingtravel-time tomography for the 645-m long AWD seismic

line. The black dotted line indicates the trend of low-

velocities (the interpreted ejecta blanket). Approximate

outcrops or surface lithologies along the AWD line are

also plotted at the top of the velocity profile. The velocity

model is plotted from the ground surface (0 m).

123


et al., 1975), 2) the 2-D S-wave velocity profile, and 3) the

2-D P-wave velocity profile along the AWD line with

reference to the actual elevations.

We identify the consistent trend of thinning of the

ejecta blanket as we move away from the crater rim in:

1) 2-D velocity models for P- and S-wave (velocities

increase with distance from the crater rim), and 2) 2-D

density model and residual gravity field studies (density

increases away from the crater). The surface lithological

expression is mostly alluvium. Debris from the Moen-

kopi and some occasional patches of the Kaibab and

Coconino at surface are observed along the AWD line.

Conclusions

A seismic investigation of the shallow subsurface

was undertaken for Barringer (Meteor) Crater, Arizona.

We produced both P- and S-wave near-surface velocity

models. We estimated P-wave velocities of 450–

2,500 m/s for a 55-m deep model. The P-wave velocity

structure shows some thinning of the low-velocity layer

as we move away (southward) from the crater rim.

P-wave velocities (varying from 800–1,600 m/s) of

Moenkopi hand specimens obtained from ultrasonic

measurements are consistent with the refraction results.

Using surface-wave inversion (MASW), we obtained

S-wave velocities from 200–700 m/s for the top 16 m,

increasing to 900–1,000 m/s at 38-m depth. We found a

prominent change in S-wave velocities (at around 500–

600 m/s), which we interpret as the transition between

the overlying ejecta blanket and the underlying bed-rock

Moenkopi. This transition is observed at a depth range

varying between 12–20 m near the crater rim (up to 800–

900 m from the center of the crater) and tapers away

Figure 6. Dispersion curves for single shot gathers from (a) the hammer line for an offset range of 9–55 m from the

source, and (b) the AWD line for an offset range of 10.5–82.5 m from the source. The plots also show phase velocity picks

for the fundamental and first higher modes.

124


(transition depth as shallow as 5 m and less) as we move

southward. The tapering trend of low-velocity layers for

both P- and S-wave velocity models is caused by the

expected thinning of the ejecta blanket away from the

crater rim, along with some local topographic effects

and local surface lithologies. Predicted bulk densities

from S-wave velocities (using a modified Gardner’s

relation) fall in the range of 1.8–2.5 gm/cm3, which are

consistent with the drilling results and some residual

gravity anomaly results. We have successfully identified

different lithological layers based on seismic velocity

variations (especially S-wave), estimated the ejecta

Figure 7. The 2-D S-wave velocity profiles determined from the surface-wave inversion for (a) the hammer line (the

profile is of 22–42 m from the total of 0–66 m line), and (b) the AWD line (the profile is of 51–609 m from the total of

0–645 m line). Approximate outcrops or surface lithologies along the AWD line are also plotted at the top of the velocity

profile. Dashed lines show our interpretation of the transition from the ejecta blanket to bed-rock Moenkopi. The velocity

models are plotted relative to ground surface (0 m).

Table 4. Summary of the depths of transition from the ejecta blanket to the bedrock Moenkopi from Roddy et al. (1975)

and surface-wave inversion method close to the crater rim (up to 800–900 m from the center of the crater).

South-East line (Roddy et al., 1975) Hammer line South line (Roddy et al., 1975) AWD line

10–19.5 m 10–14 m 13.5–18 m 15–20 m

125


blanket thickness, and also identified the thinning of the

low-velocity ejecta blanket as we move away from the

crater rim. Near-surface seismic methods as outlinedabove may be useful in the study of other meteorite

impact structures and planetary expeditions.

Figure 8. (a) A 2-D bulk density profile (from the AWD

line) predicted from the modified Gardner’s equation using

Vs and plotted relative to the ground surface (0 m), (b) the

residual gravity anomaly over the same portion of theAWD line as the density profile (Turolski, 2012).

Table 5. Summary of the dry bulk densities at differentdepths for different lithological units and the depth of

transitions (Watkins and Walters, 1966 and modified

after Kring, 2007).

Drill core: MCC-4; Location: South side of the crater, 10 m

from the crater rim

Depth (m)

Dry bulk

density (gm/cm3) Lithology

8.2 2.18 Ejecta-sandstone

9.3 2.18 Ejecta-sandstone

10.7 2.19 Moenkopi-sandstone

16.0 2.44 Moenkopi-sandstone

20.0 2.48 Moenkopi-shaly sandstone

21.0 2.68 Kaibab-dolomite

Figure 9. The 2-D a) P-wave and b) S-wave velocity

models plotted with reference to actual elevation and

interpreted thickness of ejecta blanket. c) The figureshows the transition depths (from the ejecta blanket to the

bed rock Moenkopi) from: 1) previous work (drill cores

from Roddy et al., 1975), 2) P-wave refraction analysis,

and 3) surface-wave inversion method with reference to

actual elevation profile.

126


Acknowledgments

We thank the University of Houston field crews

(especially Mr. Bode Omoboya, Mr. Li Chang, Mr. Arkadiusz

Turolski, and Ms. Tania Mukherjee) for their assistance in

acquiring the data and their analysis. We are also appreciative

of Dr. D.A. Kring of the Lunar and Planetary Institute for

helping coordinate the Meteor Crater surveys, along with the

generous staff at the Meteor Crater Museum. Dr. K. Spikes

and Ms. Jennifer Glidewell, from The University of Texas at

Austin, participated in Meteor Crater surveys.

References

Ackermann, H.D., Godson, R.H., and Watkins, J.S., 1975, A

seismic refraction technique used for subsurface inves-

tigations at Meteor Crater, Arizona: Journal of Geo-

physical Research, 80, 765–775.

Dey, A.K., and Stewart, R.R., 1997, Predicting density using

Vs and Gardner’s relationship: in Research Report:

Consortium for Research in Elastic Wave Exploration

Seismology, Ch. 9.

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