EXPERIMENT NAME:
The Missouri to Massachusetts Broadband SeismometerExperiment

NAMES OF PRINCIPAL INVESTIGATORS AND THEIR INSTITUTIONS:
Karen Fischer, Brown University
Michael Wysession, Washington University
Timothy Clarke, New Mexico Tech

START DATE OF EXPERIMENT:  January 20, 1995
DATE OF EXPERIMENT DEMOBILIZATION:  April 12, 1996

EXPERIMENT DETAILS

Number of stations:  18
Network Code and Years: XA 95-96

Station locations:
MM01  42.317500  -72.711700   122.0 Northampton, Massachusetts
MM02  42.166000  -73.718700   134.0 Hudson, New York
MM03  42.038800  -74.846200   670.5 Roscoe, New York
MM04  41.853000  -76.198000   473.0 LeRaysville, Pennsylvania
MM05  41.653000  -76.922000   701.0 Gleason, Pennsylvania
MM06  41.391500  -78.126200   647.0 Emporium, Pennsylvania
MM07  41.257130  -79.135000   518.0 Sigel, Pennsylvania
MM08  41.109500  -80.068200   381.0 Slippery Rock, Pennsylvania
MM09  40.791100  -81.205600   357.0 East Canton, Ohio
MM10  40.614700  -82.303100   346.0 Mohican State Forest, Ohio
MM11  40.221400  -83.194700   283.0 Columbus, Ohio
MM12  40.043900  -84.372500   305.0 Pleasant Hill, Ohio
MM13  39.831700  -85.311400   337.0 Straughn, Indiana
MM14  39.549434  -86.394762   290.0 Brooklyn, Indiana
MM15  39.294520  -87.313460   190.6 Terra Haute, Indiana
MM16  38.921900  -88.304570   165.0 Lake Newton, Illinois
MM17  38.669440  -89.325550   143.8 Lake Carlyle, Illinois
MM18  38.528680  -90.568600   185.6 Tyson, Missouri

Stations were installed over January-March, 1995, anddemobilized over March-April, 1996.  All sensors were installed in sub-surfacevaults, and most were powered by batteries and solar panels.  Sensors were a mix of STS-2's and CMG-3T's. 

A BRIEF SUMMARY OF THE EXPERIMENT OBJECTIVE:
In the MOMA experiment, 18 broadband seismometers were deployed betweenpermanent IRIS/GSN stations CCM (Cathedral Caves, Missouri) and HRV (Harvard,Massachusetts), providing a linear 20-station array spanning 1740 km. The goalof the experiment was to obtain new information about the structure of the core-mantle boundary (CMB), thestructure of the crust and mantle beneath the eastern U.S. (including mantlediscontinuities, mantle anisotropy, and lateral velocity variations), and thestructure of subducting lithospheric slabs.

PRELIMINARY SCIENTIFIC RESULTS:
(1) Studies of the slownesses ofcore-diffracted Pdiff and Sdiff waves across MOMA show sub-Pacific D" velocities varying by 10% for S and 7%for P.  Evidence for chemical heterogeneity or strong anisotropy is seen inlarge S/P variations, with the D" Poisson ratio varying from 0.25 - 0.32. 
(2) Interstation variations in the SdS triplicationfrom the top of D" beneath Central America show lateral variations at scalesless than 150 km. 
(3) Studies of both the change in Sdiffamplitudes as a function of distance as well as Sdiff and Pdiff dispersion (change in slowness as a function of frequency) suggest adiscontinuous velocity increase about 200 km above the CMB beneath themid-eastern Pacific underlain by a very thick (100 km) thermal boundary layerwith a strong negative gradient. 
(4) Sdiff amplitude decay rates are wellmodeled by the above velocity structure, and do not require increasedattenuation, suggesting most D" rock is well below its solidus. 
(5) Splitting in Sdiff phases has been used to map out variations inanisotropy within the core-mantle boundary region beneath the Pacific.
(6) Modeling of SPdKS phases has providedevidence for a thin (5-10 km), ultra-low velocity zone (ULVZ) just above thecore-mantle boundary beneath the central Pacific; SPdKS phases thatsample the western Pacific rim show no evidence for a ULVZ, although a very thin ULVZ cannotbe ruled out.
(5) Crustal and upper mantle variations across MOMAwere quantified using inversions of surface waves via two methods: a geneticalgorithm inversion of interstation dispersion, and a 3-D partitioned waveforminversion technique.
(7) Shear wave splitting fast directions atwestern MOMA stations located above the North American continental root areroughly parallel to absolute plate motion.  However, fast directions measured at stations in the northeastern U.S. beyond the root margin show morevariation over short spatial scales.  While this splitting may be due tolithospheric anisotropy alone, much of the observed splitting can also beexplained by asthenospheric flow.
(8) Transition zone discontinuities were imaged by Ps converted phases instacked receiver functions.  The thickness of the transition zone and the depthof the "410" discontinuity indicate that cold root material and relateddownwelling must be largely confined to the upper mantle, and may impinge on the transition zone only inlocalized regions and with thermal anomalies of less than ~150K.  A depressionof the "660" to the south of the western stations coincides with a region offast velocity in the deep transition zone, and may be associated with the remnants of the subductedFarallon plate.

RECORDING PARAMETERS:
(Number of channels, their related sample rates and type)
2 continuous channels: 20 sps and 1 sps

APPROXIMATE AMOUNT OF DATA:  60000 Mb

DESCRIBE ANY KNOWN PROBLEMS WITH THE DATA OR PARTICULARPROBLEMS ENCOUNTERED DURING THE EXPERIMENT:

Please note that the CMG-3T instrument responses in the dataarchived at the DMC were incorrect through August of 1998.  All instrumentresponses are now correct.

Data gaps related to low station power occurred at many sites,particularly during the winter months due to snow and ice accumulations on solarpanels.  Data gaps due to DAS failures were not uncommon.  

For more information on stations, please consult:
MM01-MM06 : Karen Fischer (karen@emma.geo.brown.edu)
MM07, MM08, MM15-MM18 : Michael Wysession (michael@wucore.wustl.edu)
MM09-MM14 : Tim Clarke (clarke@griffy.nmt.edu)

MM01: STS-2
The GPS clock at MM01 did not lock from 95:223-95:279 andtiming during this period is unreliable.

MM02: CMG-3T
The instrument response of the CMG-3T installed at MM02 (serialnumber T302) differs from the other CMG-3T's in the array. 

MM03:  CMG-3T
The sensor was installed on 95:041, but was pulled out on95:078 due to flooding in the vault.  A new vault with drainage ditch wasconstructed nearby and the sensor was reinstalled on 95:114.

MM04: CMG-3T through 95:186, STS-2 thereafter
On 95:187 the original CMG-3T sensor was replaced with an STS-2 to accommodatePASSCAL hardware needs.  Unfortunately, the STS-2 was incorrectly mixing itsmass motions and the relative amplitudes and waveforms on the N, E and Zcomponents were in error from this point through the end of the deployment.  Spurious electronic noisebecame more apparent towards the end of the experiment.

MM05: CMG-3T

MM06: CMG-3T

MM07: CMG-3T
On 95:266, the vault showed evidence of having had water up to half the heightof the CMG-3T sensor. No data were obtained during 95:330-95:365 due to ice andsnow on the solar panel. On 95:310 the sensor pier raised. On 96:041 the sensorwas manually releveled, and water was up to 2/3 of the height of the CMG-3T.

MM08: STS-2
On 95:265 the vault showed evidence of prior flooding.  On96:041 the sensor was manually releveled.  Water was at the vault bottom belowthe pier and the drain pipe.

MM09: STS-2

MM10: STS-2

MM11:  CMG-3T
The original clock installed on 95:059 failed to lock properly.  Timing issuspect from 95:059 to 95:095 when a new clock was installed.  CMG-3T sensorneeded manual releveling on 95:095.  Site was found to be flooded on 95:181 and95:194, but was dry on 95:245.  The sensor pier was raised on 95:308.  Flooding probably occurred around96:059.

MM12: STS-2

MM13:  STS-2
The station was installed on 95:027, but a malfunctioning DASkept it largely shut down until the DAS was replaced on 95:116.  On 95:247 theSTS-2 borrowed from the JSP was replaced by a PASSCAL STS-2.

MM14: STS-2
The original clock installed on 95:082 failed to lock properly.  A new clock wasinstalled on 95:095, but timing is suspect from 95:082 to 95:124 when the powersupply was replaced.  On 95:247 the STS-2 borrowed from the JSP was replaced bya PASSCAL STS-2.

MM15:  STS-2
The site was found to be flooded on 95:104. There was no datafor this site from 95:104 to 95:229.  Sensor was manually releveled on1996:037.

MM16: STS-2

MM17: STS-2
Data from this site during 95:120 - 95:145 are questionable, asthe site may have been flooded. No data exist for 95:145-95:173 due to flooding.On 95:173 the STS-2 borrowed from the JSP was replaced by a PASSCAL STS-2.

MM18: STS-2
On  96:025 this station was moved to a new site (a bunker)within the general area and renamed mo18.  Determination of N inside the bunkerwas difficult, so errors in sensor orientation might be  somewhat larger than at other sites.  Thesensor was manually releveled on 95:234.

PRELIMINARY LIST OF PUBLICATIONS:

Li, A., K. M. Fischer, M. E. Wysession, T.J. Clarke. Mantle discontinuities and temperature under the North Americancontinental keel, Nature, , 160-163, 1998.

Wysession, M. E., A. Langenhorst, K. M. Fischer, G. I.Al-Eqabi, P. J. Shore, M. J. Fouch, T. J. Clarke, Mantle flow inferred fromlateral variations in compressional/shear velocities at the base of the mantle,Science, submitted, 1998.

Wysession, M. E., K. M. Fischer, T. J. Clarke, G. I. Al-eqabi, M. J.Fouch, L. A. Salvati, P. J. Shore, R. W. Valenzuela, Slicing into the Earth:Seismic mapping with the Missouri-to-Massachusetts broadband deployment, , 77, 477, 480-482, 1996.

Fischer, K. M., M. E. Wysession, T. J. Clarke, G. I. Al-eqabi, M. J.Fouch, L. A. Salvati, P. J. Shore, R. W. Valenzuela, TheMissouri-to-Massachusetts broadband deployment, IRIS Newsletter, 15, 6-9,1996.