Status report to CoCom and Board of Directors
EarthScope Transportable Array
RW Busby, 15 April 2013, revised 26 April 2013
Executive Summary
Transportable Array is operating well within budget and schedule targets. Transportable Array ended
Y5 month 5 (February 2013 close) of five year Cooperative Agreement with a positive cost variance
(underspent) of 5% of annual budget, a variance of $548k. The project did not rebaseline in Year 3 or
Year 4 but had informally agreed with NSF in Y3 to carry forward $1.1M into Y5 for contingent
activities. In terms of schedule, operations are on plan: installation and construction are 7 stations
behind (9 days) the plan due to wet ground, permitting is 12 stations from completion, removal is on
plan (including removing some straggler vaults). TA has pursued contingent activities related to
deployment in Alaska that includes installation of five test stations, permitting activity on four
additional stations this summer. TA has established a warehouse/office facility in Anchorage staffed
by a new HTSI position, Alaska Deployment Coordinator Brian Coyle. The TACO Station Coordinator,
Steve Welch, retired in Dec 2012 and the position will not be filled. A new subaward is nearly in place
with University of Alaska Fairbanks which would support three full-time positions. Cascadia and
Reference Array station operation has been nominal.
Report
Budget Status
Transportable Array ended Y5 month 5 (February 2013 close) of the five year Cooperative Agreement
with a positive cost variance (underspent) of 5% of annual budget, a variance of $548k. The Current
Year Spend Plan (CYSP) for year 5 of the Cooperative Agreement is shown below. A number of
projected Alaska Operations tasks have yet to be reclassified from construction and permitting
TA Status report 4/26/2013
Page 1
Y5 Projections
as of Feb 2013 Close
3.4.2 Transportable Array
3.4.2.1 TA Management
Y5 Funding
584,111
3.4.2.2.1 TA Maintenance/Repair/Replacement 1,900,480
REVENUE FROM ADOPTED STATIONS
(152,680)
Sep-12
adjustments
Carryover between tasks
(6,542)
247,417
(935,648)
112,159
1,381,469
(112,159)
42% of period
CFY actuals / Projected total
Total
Available
824,986
Total
Projected
590,392
2,346,301
2,431,919
(152,680)
(222,845)
estimated
variance
234,594
(85,618)
CFY Actuals
229,735
39%
Y4
Actuals
861,269
837,687
34%
2,015,838
70,165
(32,225)
(178,459)
3.4.2.2.2 TA Alaska Facilities
-
-
-
-
46,838
(46,838)
62,595
134%
3.4.2.2.3 TA Alaska Operations
-
-
-
-
343,763
(343,763)
152,640
44%
3,887,262
(172,797)
1,392,368
36%
3,135,562
607,659
3.4.2.3 Array Operations
-
3,472,106
1,265,019
(1,022,659)
3.4.2.4 Station Deployment
3.4.2.4.1 Removals
515,188
672,692
(612,342)
575,538
656,688
(81,149)
326,766
50%
3.4.2.4.2 Permitting
857,046
880,599
(234,934)
1,502,711
1,218,351
284,360
281,962
23%
912,552
(187,275)
522,011
1,899,821
1,829,096
70,724
584,386
32%
1,879,067
1,107,304
486,971
(280,961)
10,001,320
2,175,816
3.4.2.4.3 Construction
3.4.2.4.4 Installation
3.4.2 Transportable Array
1,565,085
0
3,714,465
-
1,313,315
1,323,225
(9,911)
719,959
54%
950,275
12,177,137
12,327,534
(150,397)
4,588,098
37%
10,362,222
The project did not re-baseline in Year 3 or Year 4 but had informally agreed with NSF in Y3 to carry
forward $1.1M into Y5 for contingent activities. Projections to year-end forecast a $150,00 overspend
on TA and $50,000 on Cascadia.
A key to accurate projections for year end spending and the overall cost management of the project is
tracking unit costs against plan. The table below shows the planned unit costs and the chart gives an
estimate of actuals for the last two years. The budget versus actuals for construction suffers from an
accounting issue where the stated budget does not include IRIS costs, only subaward budgets. The
budget is closer to $11,000.
per/ station $
Removals
Construction
Installation
TA Status report 4/26/2013
Trend, 2 years
budget
Actuals
$3,000
$3,600
$7,000
$9,200
$4,250
$4,250
Page 2
$20,000
$18,000
$16,000
Construction unit cost
$14,000
$12,000
$10,000
Install Unit cost
Removal Unit cost
$8,000
$6,000
$4,000
Linear (Construction unit
cost)
Linear (Install Unit cost)
$2,000
$-
Linear (Removal Unit cost)
Schedule Status
As of April 14, operations are on plan: installation and construction are 7 stations behind (9 days) the
plan due to wet ground, permitting is 12 stations from completion, removal is on plan (including
removing some straggler vaults).
The planned installation schedule is overlain on a current TA status map as of 4/9/2013
TA Status report 4/26/2013
Page 3
TA Status report 4/26/2013
Page 4
Cascadia and Reference Array station operation has been nominal.
In Cascadia, a maintenance episode is planned for the summer to refresh batteries and, where
necessary, replace media sticks at all stations. A new battery design will be implemented that
changes the large reserve batteries from single use alkaline to rechargeable AGM lead acid. This has a
higher initial cost but reduces annual service visits in the SAGE budget. That expense will likely
exhaust ARRA funds for this project.
Y5 Projections
as of feb 2013 close
Transportable Array -Cascadia
Y5 Funding
7,101
Total
Available
64,460
Total
Projected
1,387
DMC
24,997
27,110
32,493
(5,384)
TA Maintenance/Repair/Replacement
41,959
97,410
59,354
38,055
138,881
77,010
183,961
(106,951)
76,031
35,907
(57,494)
35,907
TA Management
Array Operations
estimated
variance
63,072
CFY Actuals
1,387
12,999
(132,271)
3.4.2.4 Station Deployment
Construction
-
(21,587)
Installation
-
(15,164)
Transportable Array -Cascadia
212,938
261,035
(5)
313,098
(15,159)
(5)
(52,062)
(5,952)
Contingent Activities
Canada deployment will continue this summer, subject to approval by NSF, deploying 28 additional
stations. The geographic area is smaller this year and the stations not quite as remote as some last
year. Procedures for transiting the border for crew and equipment are expected to be simpler due to
existing work permits and custom broker arrangements.
TA has pursued contingent activities related to deployment in Alaska that includes installation of five
test stations (see report Appendix A) and additional dialogs with stakeholders including BLM, NOAA
and ATWC, and the AEIC at University of Alaska Fairbanks. An additional contingent activity was the
purchase of a helicopter portable drill capable of auguring or coring holes to 8” diameter, but this has
not been delivered.
Meetings and Presentations
AGU Fall Meeting 2012
American Meteorological Society, Jan 2013
PGC Victoria, GEM workshop Vancouver, Feb 2013
Polar Technology Workshop, April 2013
European Geophysical Union, April 2013
TA Status report 4/26/2013
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Seismological Society of America April 2013
Activities of Governance Committee
(3) TAWG webinar presented
(1) TAWG status briefing
USAAC last met Dec 1-2 2012. Reports from that meeting are presented separately by USArray Director.
A conference call was held April 15 to review status, spend down plans and provide input on governance
recommendations. Considerable discussion focused on input to the TA Scope Management Plan that
identifies community priorities in the operational choices available to USArray management to address
cost and/or budget pressure.
Activities related to NSF
Property transfers have been completed related to station adoptions in Arkansas, Ohio, Purdue and
Yukon.
A meeting at EAR Division Director Wendy Harrison’s office on Feb 15 to discuss integration with Polar
Programs and a follow-on meeting with the Division director of Atmospheric and Geospace Sciences
Michael Morgan. 6 hours later the Chelyabinsk Meteor exploded to produce the largest infrasound
source in recent history, fittingly an atmospheric event by a geospace object. In the subsequent days a
special event page was produced by IRIS DMC
http://www.iris.edu/dms/nodes/dmc/specialevents/2013/02/19/chelyabinsk-russia-bolide-meteor/ and
this was followed by an NSF press release
http://www.nsf.gov/news/news_summ.jsp?cntn_id=127114&WT.mc_id=USNSF_51&WT.mc_ev
=click
Several discussions related to CEUSN; USGS in January, NSF in Feb and several phone/emails
Media and others
The TA hosted a delegation from ChinArray December 14 at IRIS HQ and a visit to station O55A in PA Dec
15.
The Weather Channel filmed installation of S59A Friday April 12. This aired April 26, on “Good Morning
with Al”.
A congressional and NSF site visit is planned to Q59A near Annapolis MD on May 2.
TA Status report 4/26/2013
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Appendix A: Sensor Burial Tests Report – Second edition
Updates from POKR POKR.01, HDA, TCOL, EPYK, TASN, TASO
DRAFT: Sensor Emplacement Tests for TA Seismic Stations in Alaska
By: The IRIS Instrumentation Services Team
In preparation for redeploying EarthScope’s USArray Transportable Array (TA) to Alaska
beginning in 2014, IRIS has been exploring new strategies for sensor emplacement. These
efforts are necessitated by the conditions unique to operating in Alaska, where sparse road
access limits available equipment and hardware at sites, and permafrost may prevent the
widespread use of the standardized TA vaults that have been used successfully across the
lower-48. This work is also motivated by the recent availability of several models of broadband
seismometers designed for shallow boreholes. Replacing the TA vault sensors used in the
lower-48 with these instruments will be a major cost driver for the seismic component of
EarthScope in Alaska which is accounted for in the replacement equipment from the CEUSN
project. To this end, we have undertaken several tests to evaluate the placement and
performance of these types of sensors in various emplacement scenarios. The primary goals of
this work are to; 1) develop a procedure for reliably and economically deploying these
seismometers; 2) understand the limitations and advantages of shallow boreholes; and 3)
maintain or improve the high standard of both quantity and quality of data produced by TA
stations in the lower-48. In this report we describe the current performance of TA stations,
discuss several borehole sensor emplacements, and present the initial results of these studies.
Evaluating a TA station’s performance uses a probability density function (PDF) created by
combining the power spectral density (PSD) values calculated from one hour segments of
continuous seismic records (McNamara and Buland, 2004). This shows the characteristic
spectra recorded by each channel of a seismometer, ideally for a station deployment
encompassing multiple seasons. The result for a single channel maps the probable occurrence
of power as a function of period for the signal, emphasizing the sensitivity of the station to
background noise spectra as energy from earthquakes and short-term instrument signal recede
into the background probability. In North America quiet stations show spectra that reside close
to the global low noise model (Peterson, 1993) but conform to a somewhat higher minimum low
noise model (McNamara and Buland, 2004) and have probabilities that concentrate along a
narrow range of signal power (Figure 1). The character is significantly different between vertical
and horizontal components. Signal power exhibits a strong frequency dependence coinciding
with the oceanic microseism that is prevalent at periods between approximately 5 and 15
seconds and forms a broad peak 20-40 dB higher than the adjacent spectrum. Stations with
relatively quiet spectra outside the microseism will effectively record local and regional
seismicity and research-grade teleseismic arrivals, respectively, producing data ideal for the
community to fulfill the primary scientific objectives of the USArray.
TA Status report 4/26/2013
Page 7
Figure 1: From McNamara and Buland, 2004. A characteristic PDF plot of summed PSD estimates for a
broadband seismometer (left) and minimum noise levels measured from PDFs for stations in the USNSN
and ANSS (right).
Lower-48 Station Performance
The mean behavior of the lower-48 TA shows expected seasonal (Figure 2) and geographic
(Figures 3 and 4) variations in its signal. Microseismic noise coincident with oceanic storms in
the northern hemisphere is 20-30 dB stronger during the winter (Figures 2 and 3). Short period
noise is slightly stronger in the summer, probably due to wind, thawed ground, and increased
human activities, particularly in rural fields where the stations are predominantly located. Long
period signal appears to correlate seasonally as well, mirroring the microseismic behavior.
While the spectral characteristics of the horizontal and vertical channels are generally similar,
signal is ~20 dB stronger on horizontal channels and thought to be related to the admittance of
atmospheric pressure variations which produce a tilt on the sensor. This suggests that
conditions of the sensor emplacement and potential insulation from pressure variations should
have a strong affect on horizontal noise levels.
TA Status report 4/26/2013
Page 8
Figure 2: Power measurements for five representative periods averaged for all TA stations and plotted as
a function of time (left) and as a histogram (right). Sensitivity to long period noise (green) distinguishes
the behavior of signal power on horizontal channels when compared to the vertical channel.
Signal power at TA sites shows regional trends. Relative to the lifetime mean TA performance,
stations in the intermountain west were the quietest, residing about 5-10 dB below average in
January and 15-20 dB below average in August for long period signal. Stations in the Ohio and
Tennessee Valleys also perform near this level. Coastal stations are quieter at long periods
during the summer but appear less sensitive to this seasonal variation. In contrast, stations
across the Great Plains, Mississippi Valley, and Gulf Coast exhibit noise at least 5-15 dB higher
than average throughout the year. Across the array, short period noise is seasonally consistent
at 20-25 dB above average along the coasts and the northern Great Plains but 15-20 dB below
average within the intermountain west. Improved noise performance along the easternmost TA
stations may result from switching to a watertight, rotomolded tank design to prevent occasional
instances of flooding. The TA station quality in much of western North America demonstrates
the advantage of operating in a sparsely populated and utilized region, while proximity to natural
(ocean) or anthropogenic (agriculture) noise results in a lower station performance.
Figure 3: Residual power measurements for January (left) and August (right) at 6.4 seconds period
following removal of the mean power measurement for the lifetime of the TA. These performance trends
can be further explored here: http://crunch.iris.washington.edu/stationinfo/historic_station_ranking_Jan/
http://crunch.iris.washington.edu/stationinfo/historic_station_ranking_Aug/
TA Status report 4/26/2013
Page 9
Figure 4: Residual power measurements for January (left) and August (right) at 102.4 seconds period
following removal of the mean power measurement for the lifetime of the TA.
Test Stations
Since August 2011 six stations, operating eight seismometers, have been deployed in
Alaska/Yukon to evaluate installation procedures and noise performance of shallow borehole
sensors. In addition, a set of 5 boreholes and two cored holes have been created at ASL in
which we have tested 14 separate installations of sensors-typically with four operating
simultaneously. One additional test station was established (TA.TFRD) within the Anza array in
southern California that compared a surface outcrop STS-2 versus a 1.5m cored hole into the
outcrop. The station operated for six months and removed.
TOLK
The site at Toolik Lake Field Station on the North Slope of Alaska functions as a prototype for
Alaskan TA stations. The surface geology consists of alluvium and permafrost overlain by an
artificial 1 m thick gravel pad. Three 12” holes were augered and cased with PVC pipe. The pipe
is divided into two segments, decoupling the lower segment containing the sensor from any
movement imparted on the upper segment by the freeze-thaw cycle of permafrost. A CMG3T
sensor was lowered into two of the holes and oriented. The station experienced two months of
downtime due to power issues in its first and second winter but otherwise the seismometer has
operated continuously since being installed. PDF-PSD estimates show that especially for long
period horizontal noise, TOLK is the quietest overall stations in the entire TA (perhaps yielding
to POKR, also in Alaska). Although emplaced at different depths, both sensors produce
essentially the same response. The station performs very well during the winter at over 25 dB
below the TA average. This may be due to the frozen overburden isolating the influence of
pressure changes on sensor tilt. This effect moderates in the summer, shown by an increase in
long period noise, but is still ~10 DB below the average. The station is noticeably quieter at
short periods than the Alaskan GSN borehole seismometer COLA (Figure 5) emplaced at 120 m
depth. In the summer, both the long period and short period noise increases, whereas the
microseism noise is stronger in the winter (see figureThere is more variability due to the
aforementioned seasonal response at TOLK, but both the long period and short period
responses are ~10 dB lower on average.
TA Status report 4/26/2013
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Figure 5: Comparison of PDF-PSD estimates for 2012 from all three channels at TOLK and COLA.
Figure 6. An 18 month timeseries of discrete spectral bands for the side by side borehole sensors at TOLK.
TA Status report 4/26/2013
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Table 1: TA Stations operating or planned in Alaska and Yukon.
Station
Location
Hole Type
Sensor
TA.TOLK.--
Toolik Lake, AK
TA.TOLK.01
Toolik Lake, AK
TA.TCOL.--
CIGO, Fairbanks,
AK (adjacent to
COLA)
CIGO, Fairbanks,
AK (adjacent to
COLA)
Harding Lake AK
(replaced AK.HDA)
Poker
Flat
Research Range,
AK
Poker
Flat
Research Range,
AK
Poker Flat, AK
Eagle Plains, YT
Sachs Harbor NWT
Paulatuk, NWT
Barrow AK
Middleton Is. AK
Augered
12”
PVC
casing
Augered
12”
PVC
casing
Augered 8” PVC casing
TA.TCOL.01
TA.HDA.-TA.POKR.--
TA.POKR.01
YE.PIC3.01
TA.EPYK.-TA.A36M
TA.C36M
TA.A21K
TA.Q23K
Started
CMG3T
Depth
(m)
5
CMG3T
4
8/13/2011
STS-4B
10
10/9/2011
Augered 8” PVC casing
STS-4B
5
10/9/2011
Augered 8” PVC casing
T120PH
5
10/4/2012
TA Tank into rock
T240
2
10/12/2012
Augered 8” PVC casing
T120PH
5
10/12/2012
Hand dug, 1M
Cored in rock
6” PVC
6” PVC
6” PVC
6” PVC
T120PH
T120PH
T120PHQ
T120PHQ
T120PHQ
T120PHQ
1M
1.4
5M
5M
3M
5M
10/15/2012
5/2013
5/2013
6/2013
8/2013
8/13/2011
Figure 7 Location of Test stations in Alaska and Yukon
TA Status report 4/26/2013
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Figure 8 Two month PDF comparison of TA Tank and a 5M posthole located at Poker Flat Research Range, near Fairbanks.
Below shows performance of an additional 1M direct buried posthole sensor. As temperatures have warmed, the
performance of the 1M hole has degraded considerably due to pressure induced tilts.
TA Status report 4/26/2013
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Figure 9 Performance of a 1.5m cored hole just off the Dempster "Highway" near Eagle Plains Yukon.
TA Status report 4/26/2013
Page 14
Testing of posthole and borehole sensors at ASL
A suite of five postholes and two cored holes were created at and in cooperation with
Albuquerque Seismological Laboratory, New Mexico. These stations are adjacent to GSN
station ANMO that contains KS54000 primary and CMG3T secondary sensors buried at 145 m
and 57 m depths, respectively.
TA Status report 4/26/2013
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New US Array/ASL Boreholes
Existing
ANMO
Pad
N
10.0'
E
W
S
3m
6" ID
PVC
Casing
180"
5m
6" ID
PVC
Casing
5m
6" ID
PVC
Casing
10m
6" ID
PVC
Casing
5m
8" ID
PVC
Casing
36"
108"
108"
3" Steel
Conduit
Existing 5' X 5' ID Pit, 5' Deep
(6' X 6' Outside dimension)
36"
30"
New Solar Panels
30m
7" OD
Steel
Casing
36"
60m
7" OD
Steel
Casing
132"
Station TASM uses augered holes in diameters of 8” and 6” diameters but is otherwise similar to
TOLK with seismometers at 5 and 10 meters depth in alluvium. Station TASL utilizes holes
TA Status report 4/26/2013
Page 16
cored 6” or 8” inches diameter and ~48” deep into fractured Precambrian Granite. These holes
were drilled with a portable coring machine, which is small enough in size and weight to be
transported in a pickup truck or via fixed-wing aircraft and/or helicopter to sites throughout
Alaska. The coring procedure requires a relatively stable surface, about 10 gallons of recyclable
water, and three hours of work depending on site conditions. The direct emplacement of the
seismometer in hard rock may avoid upheaval of the instrument due to changes in permafrost,
complications with PVC casing, and should provide good coupling with the surrounding
environment. Preliminary results show that although TASL and TASM do not perform to the
level of ANMO’s deep borehole sensors, at long and short periods they equal or slightly exceed
the performance of TA station W23A, installed nearby in a traditional vault from 2008-2010
(Figure 6).
Figure 6: Comparison of PDF-PSD estimates for 2012 from the BHN/BH2 channels at TASL, TASM,
ANMO (00-KS54000), and TA station W23A. Plots from TASL/TASM reflect an artifact from temporary
application of digitizer preamps which were not included in the metadata.
TFRD
TFRD is cored similarly to TASM and installed adjacent to AZ network station FRD, which
resides in a surface vault that is subject to large temperature variations. The cored hole exceeds
the long period performance of the AZ station by 30 dB (Figure 7), showing a dramatic
improvement in the overall response obtained at this location.
TA Status report 4/26/2013
Page 17
Figure 7: Comparison of PDF-PSD estimates for 2012 from the BHN channels at FRD and TFRD.
Future Work
The TA plans to install additional test stations in the Alaska / Yukon work area to further
investigate sensor emplacement, especially concerning effects of freezing and thawing. These
stations are listed in Table 2 above, all data is available from the IRIS DMC. Metadata in some
instances may temporarily not reflect actual operation and fine details of sensor swaps and
details of the emplacement are available upon request.
References
McNamara, D.E., and R.P. Buland (2004), Ambient Noise Levels in the Continental United
States, Bull. Seismol. Soc. Amer., 94, 1517–1527.
Peterson, J. (1993), Observation and Modeling of Seismic Background Noise, U.S. Geol. Surv.
Tech. Rept., 93-322, 1–9
TA Status report 4/26/2013
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