Ashumet

Pond

Snake

Pond

41°42'30"

41°32'30"

70°27'30"

Massachusetts

Military

Reservation

41°30'

42°30'

73° 100,000

950,000

850,000

270,000

835,000

815,000

280,000

200,000 71°

0

0

50

50

MILES

KILOMETERS

MASSACHUSETTS

CAPE COD

70°37'30"

BUZZARDS BAY

CAPE COD

BAY

VINEYARD SOUND

NANTUCKET SOUND

CAPE COD CANAL

ATLANTIC

OCEAN

U.S. Geological Survey digital data

Universal Transverse Mercator projection

Zone 19, 1:24,000, 1991; State plane coordinate

system datum is the North American Datum

of 1983 (NAD 83) in meters

SANDWICH

MASHPEE

BOURNE

FALMOUTH

BARNSTABLE

5 MILES

5 KILOMETERS

0

0

Ratio of averaged-horizontal to vertical amplitudes (HVSR)

Mean

Upper and lower limits 

of one standard deviation

EXPLANATION

Frequency in Hertz (Hz) 

Peak at 1.06 Hz 

60 seconds

North-South

East-West 

Vertical

Suggested citation: 

Fairchild, G.M., Lane, J.W., Jr., Voytek, E.B., and LeBlanc, D.R., 2012, Bedrock topography of 

western Cape Cod, Massachusetts, based on bedrock altitudes from geologic borings and 

analysis of ambient seismic noise by the horizontal-to-vertical spectral-ratio method: U.S. 

Geological Survey Scientific Investigations Map 3233, 1 sheet, maps variously scaled, 17-p. 

pamphlet, on one CD–ROM. (Also available at http://pubs.usgs.gov/sim/3233.)

References cited on this plate are listed in the accompanying pamphlet. 

QR Code

Bedrock Topography of Western Cape Cod, Massachusetts, Based on Bedrock Altitudes from Geologic Borings and Analysis of 

Ambient Seismic Noise by the Horizontal-to-Vertical Spectral-Ratio Method 

By 

Gillian M. Fairchild, John W. Lane, Jr., Emily B. Voytek, and Denis R. LeBlanc

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3233

Pamphlet accompanies map

Prepared in cooperation with the 

Army National Guard and the

Air Force Center for Engineering and the Environment 

B

A

Seismometer 

under bucket

GPS

Battery

Computer

B

ourn

e

R.

Coonamessett R.

Backus

R.

Quashnet

R.

Mashpee

River

Santuit River

Child R.

Johns

Pond

Ashumet

Pond

Snake

Pond

Peters

Pond

Santuit

Pond

Coonamessett

Pond

Wakeby Pond

Mashpee

Pond

Round

Pond

Long

Pond

Crooked

Pond

Jenkins

Pond

Flax

Pond

Mystic

Lake

Middle

Lake

Hamblin

Lake

Moody

Pond

OOMW0584

Green

Pond

Waquoit

Bay

0 15,000 30,000 FEET

0 3,900 7,800 METERS

0 15,000 30,000 FEET

0 4,000 8,000 METERS

850,000 900,000

225,000

300,000

70°40' 70°30'

41°45'

41°30'

Cape

Cod

Canal

-250

-225

-175

-275

-200

-300

-1

50

-325

-350

-125

-375

-400

-75

-425

-100

-225

-150 -125

-225

-175

-225

-200

-200

-250

-150

-275

-150

-375

-150

-125

-200

-125

-225

-1

00

-75

-175

-275

-125

-225

-250

-175

-125

-225

-200

-1

25

-250

-200

-125

-1

75

-350

-275

-200

-150

-225

Base from USGS and MassGIS sources, North American Datum of 1927 (NAD 27) 

Altitudes relative to the National Geodetic Vertical Datum of 1929 (NGVD 29)

-250

-250

-250

-200

-250

-225

-225 -250

-200

-200

-200

-200

-225

-225 -225

-200

-200

-200

-200

-225

-225

-250

-275 -300

-300

-275

-250

-250

-275

-275

-250

-175

-200

-175

-275

-175

-175

-150

-125

-175

-175

-125

-200

-200

-125

-125

-125

-150

-150

-150

-175

-175

-175

-125

-150

-300

-300

-375

-400

-425

-425

-325

-325

-325

-375

-350

-350

-350

-275

-350

-275

-275

-275

-225

-225

-225

-250

-275

-300

-300

-225

-225

-200

-200

-175

-175

-150

-125

-125

-150

-175

-125

-125

-150

-175

-175

-150

-150

-150

-175

-200

-225

-250

-250

-225

-175

-275

-275

-200

-150

-125

-175

-200

-150

-125

-150

-150

-100

-75

-275

-250

-225

-200

-375

-400

-200

-225

-250

-150

-125

-350

-175

-100 -200

-125

-150

-200

-250

-200

EXPLANATION

Altitude of bedrock surface

High -50 feet

Low -450 feet

Altitude contours—relative to

 sea level, interval is 25 feet, 

 datum is NGVD 29

Town boundary

Massachusetts Military Reservation boundary 

Pond shoreline

Ocean coastline

Location of well 00MW0584 

 on eastern shore of Johns Pond

00MW0584 

SANDWICH

MASHPEE

BOURNE

FALMOUTH

MASSACHUSETTS

MILITARY

RESERVATION

Woods Hole

BUZZARDS BAY

CAPE COD

BAY

VINEYARD 

SOUND

NANTUCKET

 SOUND

BARNSTABLE

http://pubs.usgs.gov/sim/3233/

862,500 70°32' 870,000 70°30'

250,000

260,000

41°43'

41°42'

41°41' Snake 

Pond

-140

-130

-120

-160

-150

-160

-140

-170

-170

-150

-120

-150

-140

-170

-160

-170

-130

-160

-170

-160

-120

-110

-100

-150

-140

-140

-160

-130

-130

-130

-170

-160

-170

-150

-140

-150

0 2,000 4,000 FEET

0 500 1,000 METERS

EXPLANATION

Altitude of bedrock surface

High -100 feet

Low -185 feet

Altitude contours—relative to

 sea level, interval is 10 feet, 

 datum is NGVD 29

Pond shoreline

-160

EXPLANATION

High -120 feet

Low -280 feet

0 2,000 4,000 FEET

0 500 1,000 METERS

Altitude of bedrock surface

Altitude contours—relative to

 sea level, interval is 10 feet, 

 datum is NGVD 29

Pond shoreline

850,000 70°34' 860,000 70°32'

230,000

240,000

41°40'

41°38'

Ashumet

Pond

-180

-140 -130

-130

-170

-140

-180

-190

-150

-150

-150

-170

-160

-160

-170

-180

-160

-150

-120

-120

-140

-190

-190

-170

-200

-180

-210

-220

-160

-150

-160

-170

-230

-240

-180

-170

-150

-160 -140

-190

-120

-130

-200

-170

-210

-160

-140

-180

-170

-140

-130

-150

-180

-170

-190

-190

-210

-230

-190

-160

-150

-140

-170

-170

-150

-170

-230

-220

-210-200

-260

-190-180

-170

-200

-220

-230

-240

-190

-210

-130

-180

-160

-190

-210

-220

-250

-260

-250

-240

-230

Introduction

 This report presents a topographic map of the bedrock surface beneath western Cape Cod, Massachusetts, 

that was prepared for use in groundwater-flow models of the Sagamore lens of the Cape Cod aquifer. The 

bedrock surface of western Cape Cod had been characterized previously through seismic refraction surveys 

and borings drilled to bedrock. The borings were mostly on and near the Massachusetts Military Reservation 

(MMR). The bedrock surface was first mapped by Oldale (1969), and mapping was updated in 2006 by the 

Air Force Center for Environmental Excellence (AFCEE, 2006). This report updates the bedrock-surface 

map with new data points collected by using a passive seismic technique based on the horizontal-to-vertical 

spectral ratio (HVSR) of ambient seismic noise (Lane and others, 2008) and from borings drilled to bedrock 

since the 2006 map was prepared.

 The HVSR method is based on a relationship between the resonance frequency of ambient seismic noise 

as measured at land surface and the thickness of the unconsolidated sediments that overlie consolidated bedrock. The HVSR method was shown by Lane and others (2008) to be an effective method for determining 

sediment thickness on Cape Cod owing to the distinct difference in the acoustic impedance between the sediments and the underlying bedrock. The HVSR data for 164 sites were combined with data from 559 borings 

to bedrock in the study area to create a spatially distributed dataset that was manually contoured to prepare a 

topographic map of the bedrock surface. The interpreted bedrock surface generally slopes downward to the 

southeast as was shown on the earlier maps by Oldale (1969) and AFCEE (2006). The surface also has complex small-scale topography characteristic of a glacially eroded surface. More information about the methods 

used to prepare the map is given in the pamphlet that accompanies this plate. 

Figure 2. The horizontal-to-vertical spectral-ratio (HVSR) method 

uses a single broadband, three-component seismometer A, to 

record ambient seismic noise from the earth’s surface. Ambient 

seismic noise is composed of microtremors caused by ocean 

waves, wind, rainfall, and anthropogenic sources such as traffic 

and industry (Ibs-von Seht and Wohlenberg, 1999). The HVSR 

method works best at locations like Cape Cod where generally 

homogeneous, unconsolidated sediments overlie consolidated 

bedrock (Lane and others, 2008). At each measurement site, the 

seismometer B, was placed firmly on the ground to ensure sufficient coupling with the earth, and data were collected for a 

minimum of 30 minutes. 

Figure 4. The fundamental resonance frequency at a site 

was determined by a spectral analysis of the horizontal and 

vertical components of the recorded seismic noise. The 

amplitudes of the spectra of the vertical and two horizontal 

components of the microtremors for each of the 60-second 

time intervals were calculated by the Geopsy program. The 

average of the amplitudes for the horizontal components was 

divided by the vertical component, and this ratio (the HVSR) 

was plotted as a function of frequency. The colored lines in 

this graphical output from the Geopsy program correspond to 

the similarly colored time intervals shown in figure 3. The 

fundamental resonance frequency in this example from site 

00MW0584 is 1.06 Hz defined by the peak in the average 

HVSR plot (average and standard deviation shown by the 

solid and dashed black lines, respectively). An empirical 

equation (see accompanying pamphlet) developed for Cape 

Cod by Lane and others (U.S. Geological Survey, written 

commun., 2011) was used to estimate the sediment thickness 

from the fundamental resonance frequency. The resulting 

thickness was subtracted from the land-surface altitude to 

obtain the bedrock-surface altitude.

Figure 8. The interpreted representation of the bedrock surface in figure 5 is similar in its 

general features to Oldale’s 1969 map shown here and the map produced by the Air Force 

Center for Environmental Excellence (AFCEE) (2006) (not shown). In all three maps, the bedrock surface generally slopes downward to the southeast toward Nantucket Sound. The 

maps similarly show lobes of shallower bedrock extending from the vicinity of the Cape Cod 

Canal to the east toward Barnstable and to the south toward Woods Hole. The bedrock surface is more than 47 feet below NGVD 29 (sea level) throughout the mapped area and therefore does not crop out at the land surface. The general trends in altitude shown on the 

small-scale map (fig. 5) may reflect preglacial drainage patterns in the bedrock surface. The 

large-scale maps in figs. 6 and 7, however, show a surface whose altitude varies considerably over a small area. Small-scale variations, including closed depressions in the bedrock 

surface, are consistent with a glacially eroded bedrock surface (B.D. Stone, U.S. Geological 

Survey, written commun., 2011). 

Figure 1. The area of the map presented in this report is on 

western Cape Cod, Massachusetts, and includes the 

Massachusetts Military Reservation and all or parts of five 

surrounding towns. The study area is on unconsolidated 

glacial drift deposits that consist of glaciofluvial sand and 

gravel outwash overlying glaciolacustrine sand and silt, 

with sandy moraines near the northern and western 

coasts. The underlying bedrock is primarily granodiorite 

(Oldale and Barlow, 1986; Oldale, 1992). 

Figure 6. The topographic map of the bedrock surface beneath the area 

near Snake Pond was prepared with a 10-foot contour interval because of 

the closely spaced data points obtained mostly from geologic borings in this 

area. The location of the map is shown in figure 5.

Figure 3. The graphical representation of the raw data to 

obtain the depth to bedrock is shown for site 00MW0584 

(location shown in fig. 5). The graph was prepared by using 

the computer program Geopsy version 2.7.0 (Geopsy, 2011). 

The horizontal scale represents time, and the vertical scale 

represents the amplitudes of the data collected for seismic 

components in three perpendicular directions: vertical (Z), 

north-south (N), and east-west (E). The raw data were 

divided into time intervals 60 seconds long that overlap 

adjacent intervals by 30 seconds each. The small spikes in 

amplitude above the generally smooth traces were caused 

by high-amplitude noise disturbances such as the nearby 

passage of individual vehicles or pedestrians. Data from 

these intervals, which are not colored, were removed prior 

to further data processing.

Figure 7. The topographic map of the bedrock surface beneath the area near Ashumet Pond was prepared 

with a 10-foot contour interval because of the closely spaced data points obtained mostly from geologic 

borings in this area. The location of the map is shown in figure 5.

Figure 5. The bedrock-surface altitudes from the HVSR survey, seismic refraction surveys, and geologic borings that reportedly hit bedrock were plotted on a map of western Cape Cod and hand contoured with a 25-foot contour interval. This interval 

is consistent with an estimated uncertainty in the bedrock-surface altitudes from the HVSR method of about 10 percent of the depth to bedrock, or about 20–30 feet over much of the area. The altitudes from the borings have an estimated uncertainty 

of about 5 feet. The location of the map is shown in figure 1. MMR, Massachusetts Military Reservation.