APPENDIX 4

DATA REDUCTION CRUISE SUMMARY

EW-9415

LARSE Experiment:

Seismic Survey offshore Los Angeles/Northridge

Long Beach, CA - San Diego, CA , U.S.A.

10/03/94 (JD-286) -- 10/10/94 (JD-294)

CHIEF SCIENTISTS:

Thomas Brocher, USGS

(brocher@andreas.wr.usgs.gov)

SCIENCE OFFICER:

Bruce A. Francis (baf@ldeo.columbia.edu)

DATA REDUCTION:

Stefanus Budhypramono (dared@ldeo.columbia.edu)

R/V MAURICE EWING

SCIENCE OVERVIEW:

This project involved onshore-offshore seismic profiling of the crustal structure in the greater Los Angeles area, to identify and better understand the earthquake hazards of the region. The Ewing served as a source of seismic energy for both multichannel seismic reflection profiling as well as for an dense array of land stations. Three main lines were run: one through the Sierra Madre epicenter and Los Angeles Basin, one through the epicenter of the Northridge earthquake, and a third trending NE-SW through the Los Angeles basin.

TRUE TIME CLOCK:

Instrument: Kinemetric/TrueTime Division Model GPS-DC GPS Synchronized Clock
Logging: 1 minute intervals
NOTE: The True Time clock is used to adjust the CPU clock of the logging computer. The logging computer captures the continuous time records from the clock and provides these as a service to the rest of the network via a UDP broadcast. This enables the computers on the network to adjust their CPU times to UTC time.

SPEED AND HEADING:

Instrument: Furuno CI-30 2-axis Doppler speed log, Sperry MK-27 gyro
Logging: 3 second intervals
Checking: visual check of plot of data
Smoothing: mean value of all good values within the same minute

TRANSIT SATELLITE FIXES:

Instrument: Magnavox MX-1107RS dual frequency Transit satellite receiver
Logging: all fixes
Checking: reject receiver flagged fixes, fixes with high drifts in navigation

GPS SATELLITE FIXES:

Instrument: Magnavox MX-4200 Global Positioning System receiver
Logging: 10 second intervals on GPS MX-4200 #1
10 second intervals on GPS MX-4200 #2
Checking:

Interpolation: interpolated positions at 00, 30 seconds of each minute
Smoothing: smoothed interpolated positions with 9 or 41 point running average depending on the quality of GPS data and the sea state.

Note:
The GPS data has a sinusoidal wave which is assumed to come from some degrading of the GPS quality for civilian usage. This wave seems to vary in period and shapes and is not a perfect sine curve. The periods are less than 20 minutes. The amplitudes tend to vary over 24 hours and the sea state condition. This degrading produces a false ship's track in real-time navigation and introduces extreme errors, up to 10 mGals, in the Eotvos correction for the gravity. As this problem varies in its intensit y depending on the sea state and GPS data quality itself, several methods of data reduction has been developed to achieve the best possible navigation.

1. A 9 point (4 minutes) GPS smoothing
2. A 9 point (4 minutes) GPS smoothing, decimated to a 20 min. fixes
3. A 41 point (20 minutes) GPS smoothing
4. A 41 point (20 minutes) GPS smoothing, decimated to a 20 min. fixes

It should be noted that the use of 41 point smoothing causes the turn to "widens". Hence, in the instances where a 41 point smoothing is called for, the GPS data at and around the turn are decimated to 20 minutes.

Throughout this cruise, a 9 point (4 minutes) GPS smoothing, decimated to a 20 min. fixes were used to produce final navigation data.

NAVIGATION:

A "1 minute navigation" is produced from the above sources, which in this cruise is a 9 point (4 minutes) GPS smoothing, decimated to a 20 min. fixes. Acceptable fixes are merged at 1 per minute with priority given to GPS. The smooth speed and heading dat a is used to fill any gaps of 2 minutes or longer between fixes by computing 1 minute DR'ed positions corrected for set and drift between fixes. The DR'ed positions are produced at 00 seconds of each minute.

Chief scientist's final data: 1 minute navigation.

FORMAT: n.ddd
yy+ddd:hh:mm:ss.mmm N 12 12.1234 E 123 12.1234 id 123.1 12.1
yr.day time lat. lon id set drift

Lamont database: 1 minute navigation, in MGG format.

SEA TEMPERATURE:

Instrument: Omega DP10 Series
Logging: 1 minute intervals
Checking: none
Smoothing: none

Chief scientist's final data: one minute data, merged with navigation.
Lamont database: one minute data, merged with navigation.

FORMAT: ct.nddd
yy+ddd:hh:mm:ss:mmm N 12 12.1234 E 123.1234 26.3
yr day time lat lon sea_temp (in oC)

MAGNETIC:

Instrument: Varian V75 magnetometer
Logging: 6 second intervals
Checking: visual check of plot of data
Reference field: International Geomagnetic Reference Field 1990
( IGRF 1990 ) model of the main field at 1985.0 and a predictive model of
the secular variation for adjusting to dates between 1990.0 and 1995.0.
Residual field: Applied by bi-linear interpolation across a 1 degree square.

Chief Scientist's final data: final calibrated and cleaned data.

FORMAT: mg.nddd
yr+ddd:hh:mm:ss.mmm N 12 12.1234 E 123 12.1234 41200.8 -367.1
yr. day time lat lon total_intensity anomaly

Lamont Database: interpolated total intensity value at 00 second of each minute

NOTE:

ADCP (Acoustic Doppler Current Profilers):

Instrument: RD Instrument RD-VM Model ADCP
Logging: logging is done by a 386 IBM PC compatible
Checking: none
Smoothing: none

Chief scientist's final data: processed data file format and navigation data file format.
Lamont database: processed data file format and navigation data file format.

FORMAT: Refer to Transect User's Manual for Narrowband ADCP Appendix B.

BATHYMETRY:

Instrument: Krupp Atlas Hydrosweep Center Beam
Logging: At each ping of Hydrosweep, data is being broadcasted real time to
the network, which is received by data logger. The logger computer then
extracted the center beam depth.
Checking: Visual checking aided by graphic editor to remove major spikes.

Chief scientist's final data: final calibrated and cleaned center beam data, two
nearest point to the minute interpolated to even minute.
Merged with final navigation.
Depth is in meters.


FORMAT: hb.nddd
yy+ddd:hh:mm:ss:mmm N 12 12.1234 E 123 12.1234 2222.0
yr.day time lat. lon depth_in_meters

Lamont database: final calibrated and cleaned data, interpolated to even minute.
Merged with final navigation. MGG format.
Depth is in fathoms.

NOTE: At the beginning of EW-9414, a problem was found with the swath data coming out of the Hydrosweep to the logging computer "olive". An "Unknown data type" error message appeared in "get_hs" log file. Upon closer inspection, this message was generated because the data coming out of the serial line seems to be mangled if it happens to coincide with the pop of the seismic guns. It has yet to be determined whether this was caused by the shock of the guns, or it was an acoustic-interference problem.

SHOT TIME & GUN DEPTH:

Instrument: L-DEO Time Tagger and GunDepth Interface
Logging: Shot Time from the Time tagger. Gun Depth from Gun Depth Interface

FORMAT: ts.nddd (shot time)
94+173:00:04:04.333 000172 N 40 56.5884 W 125 42.6913 mcs-6a
SHOT TIMEshotnumlatlonline name
FORMAT: dg.rddd (gun depth)
94+173:00:04:04.333 13 13 13 13 13 13 13 13 ....
SHOT TIMEGUN DEPTH

Note:
A '-' sign following the year means that shottime was not received in time. A CPU timetag is placed instead. This sometimes happens at the beginning of the line when the computer and the DMS-2000 are trying to get in sync with each other. No gun was fired, and no data is recorded to the tape.

JDAY & TIME Shot Number LINE NAME COMMENTS
286:18:49:17-287:05:41:37
287:11:55:42-288:01:24:01
288:01:28:30-288:06:32:37
288:06:32:56-288:12:35:17
288:12:36:27-288:21:44:45
288:21:45:16-289:12:10:24
289:12:11:30-290:02:37:25
290:02:38:46-290:04:59:09
290:05:17:27-291:02:54:01
291:01:54:58-291:19:56:51
291:20:52:55-292:04:04:19
292:04:05:21-292:12:31:41
292:13:29:27-292:17:50:16
292:17:51:16-292:23:49:10
292:23:51:10-293:06:40:04
293:06:40:41-293:13:56:16
293:14:00:13-293:14:43:08
293:14:43:08-293:16:44:02
293:18:35:45-294:04:31:30
0101-0753
0105-2414
0101-0935
0101-1068
0101-0783
0101-2546
0101-2587
0101-0494
0101-3215
0101-0822
0101-1369
0101-1619
0101-0883
0101-1174
0101-1327
0101-1407
0101-0126
0101-0462
0101-1885
LA01
LARSE01R
LARSE01X
LARSE01Y
LARSETR1
LARSE03
LARSE03R
LARSETR2
LARSE02
LARSE02R
LARSE02X
LARSE02Y
LARSE02Z
LARSETR3
LARSE01A
LARSE01B
LARSE04
MARSE04
LARSE06
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-time 90 secs.
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m
shot-by-dist 50m

Partial CO2:

Instrument: L-DEO PCO2 Group PCO2 Analysis Instrument
Logging: as is.
Checking: none

Chief scientist's final data: none.
Lamont database: merged data with final navigation.

FORMAT:
94+036:22:35:00.000 S 21 31.0624 W 31 27.2926 94036.9360
Yr Day Hr Mn Second Lat LonYrDay.frac

WEATHER STATION:

Instrument: R.M/. Young Precision Meteorological Instruments 26700 Series
Logging: 1 minute interval
Checking: none

Chief scientist's final data: as is.
Lamont database: as is.

FORMAT: wx.rddd
Port bird is bird #1; starboard bird is bird #2.

KSS-30 GRAVITY:

Instrument: Bodenseewerke KSS-30 marine gravity meter
Logging: 6 second intervals
Merge with navigation: calculate Eotvos correction and Free Air Anomaly.
Checking: Visual check of plot of data to determine satisfactory Eotvos corrections, reject spikes of data at turns.
Velocity smoothing: 5 point running average throughout the cruise
Processing:
The KSS-30 times tag is first adjusted for the filtering delay. For "Seastate" setting 2, the delay due to filtering is 75 seconds. Thus75 seconds are subtracted from the time tag and a new, adjusted time is computed.

A smooth KSS-30 gravity mgal value at one minute interval is calculated on 00 second of the minute by computing the unweighted mean values from the raw values that lie between +-30 seconds of 00 seconds of the minute.

Calculation:
eotvos_corr = 7.5038 * vel_east * cos(lat) + .004154 * vel*vel
corrected_grv = raw_grv + eotvos_corr - drift - dc_shift
faa = corrected_grv - theoretical_grv

Chief scientist's final data: Observed, Eotvos, Free Air Anomaly value at 00 seconds of each minute.

FORMAT: vk.nddd
yy+ddd:hh:mm:ss.mmm N 10 20.1234 W 120 23.1234 1980 77.1
yr. day timelat.lon.theog FAA
979317.5 64.1 1.5 10.2 -1.7 9.7 -1.6 9.8
raw_grav eotvos drift dc_shift raw_vel smo_vel

Lamont database: Free Air Anomaly value at 00 seconds of each minute.
1930 International gravity formula.
Note:
A '-' sign after the year in the record signifies a flagged record due to turn.

As a result of the discussion among the MG&G group, Lamont Data Reduction will use Port's Gravity Referenced Value without Potsdam correction for gravity data sent to MG&G data base at Lamont.
Further discussion also revealed that 1980 theoretical gravity formula has incorporated Potsdam correction in its formula.

At the start of the cruise, KSS-30 platform was found turned off. As a result, there is no data until the start of JD 164.

BGM-3 GRAVITY:

Instrument: Bell Aerospace BGM-3 marine gravity meter
Logging: 1 second intervals
Merge with navigation: calculate Eotvos correction and Free Air Anomaly.
Checking: Visual check of plot of data to determine satisfactory Eotvos corrections, reject spikes of data at turns.
Velocity smoothing: 5 point running average throughout the cruise.
Processing:

Calculation:
eotvos_corr = 7.5038 * vel_east * cos(lat) + .004154 * vel*vel
corrected_grv = raw_grv + eotvos_corr - drift - dc_shift
faa = corrected_grv - theoretical_grv

Chief scientist's final data: Observed, Eotvos, Free Air Anomaly value at 00 seconds of each minute.

FORMAT: vt.nddd

yy+ddd:hh:mm:ss.mmm N 10 20.1234 W 120 23.1234 1980 77.1
yr. day timelat.lon.theog FAA
979317.5 64.1 1.5 10.2 -1.7 9.7 -1.6 9.8
raw_grav eotvos drift dc_shift raw_vel smo_vel

Lamont database: Free Air Anomaly value at 00 seconds of each minute.
1930 International gravity formula.

Note:
A '-' sign after the year in the record signifies a flagged record due to turn.

As a result of the discussion among the MG&G group, Lamont Data Reduction will use Port's Gravity Referenced Value without Potsdam correction for gravity data sent to MG&G data base at Lamont.

Further discussion also revealed that 1980 theoretical gravity formula has incorporated Potsdam correction in its formula.

PRE-CRUISE GRAVITY TIE-IN:

Port: Dutch Harbor, Alaska, U.S.A.
Date: July 6, 1994 (JD 187)
Operator: Bruce A. Francis
Reference Station:
ACIC 2178-1
Reference Value: 981552.07 mGals

Pier/Ship's position:
R/V Ewing was at the pier by the Delta Western Warehouse.
Moved here on July 6th to take on fresh water.

Gravity meter: L & R Model G, serial number 237.
Temperature of meter: 49 oC.
Readings and Calculations:

TIME
LOCATION
L&R READING
G
Potsdam Corr?
2015Z
Pier
5046.64+- .05


2032Z
Ref
5046.43+- .05
981552.07
NO!
2042Z
Pier
5046.62+- .05


TIME
GRAVITY
G READING
2042Z
BGM-3
981564.3
2042Z
KSS-30
1396.08

Pier reading 2.8 m above waist deck. Waist deck is 5.5 m above gravity meter.
Difference between pier and gravity meter : 5.5 + 2.8 = 8.3 m.

Lacoste difference in LR units:
delta_LR= pier_LR - ref_LR
0.19= 5046.62 - 5046.43

Difference in mgal: ( 1 LR unit = 1.06 mGals )
delta_mgal= delta_LR x constant
0.2= 0.19 x 1.06

Pier gravity value in mgal: ref_val = G (+13.6 if Potsdam corrected)
pier_grv_val = ref_val + delta_mgal
981552.27= 981552.07 + 0.2

Height correction:
Height correction in mGals:
note: free-air constant of +0.31 mGals per meter going towards
the center of earth; -0.31 mGals per meter going away.
hgt_corr= hgt x constant
2.57 mGals = 8.3 x 0.31 mGals/m

Gravity at gravity meter level in mGals:
grv_at_meter_level = pier_grv_val + hgt_corr
981554.84= 981552.27 + 2.57

KSS-30:

KSS-30 value was smooth and time adjusted by 75 secs.

KSS_grav_val = kss_unbiased_output + bias
981556.37 = 1396.08 + 980170.29

Mistie in mGals:
mistie = KSS_grv_val - grv_at_meter_level
11.53 = 981556.37 - 981554.84

Drift in mGals since last tie:
prev_mistie: 15.6 mGals on date May 20,1994 (JD 140)

drift = mistie - prev_mistie
-4.07 = 11.53 - 15.6

==> DC Shift = prev_mistie - bias
= 15.6 - 980170.29 = -980154.69
Drift/Day = drift / (tot. # of day)
= -4.07 / (187-140) = -0.0866 mGals/day

BGM-3:

BGM_filt_grv = ( scale factor x counts ) + bias = 979537.0
using s.f. 5.0940744 and bias 8526800, filter width 360. ( 6 minutes)

Mistie in mGals:
mistie = BGM_grv_val - grv_at_meter_level
9.5 = 981564.3 - 981554.84

Drift in mGals since last tie:
prev_mistie: 9.83 mGals on date May 20, 1994 (JD 140)
drift = mistie - prev_mistie
-0.3 = 9.5 - 9.83

==> DC Shift = prev_mistie
= 9.83
Drift/Day = drift / (tot. # of day)
= -0.3 / (187 - 140) = -0.0064 mgals/day

POST-CRUISE GRAVITY TIE-IN:

Port: Balboa, Canal Zone, Panama
Date: 26-27 November, 1994 (JD 330-331)
Operator: Bruce A. Francis
Reference Station:
The site is on the sidewalk on the west of the Captain of the Port building, in front of main entrance. The station was made in the middle of the circular concrete section on the sidewalk.
Date: 01 Nov. 1971 Position: N 8o 57.60' W 79o 33.81'
Pier/Ship's position:
R/V Ewing was docked at Pier 16. The tie point is midship, port side.
Gravity meter: L & R Model G, serial number 237.
Temperature of meter: 49 oC.
Readings and Calculations:
TIME
LOCATION
L&R READING
G
Potsdam Corr?
JD 330 1915Z
Pier
1919.835+- .05


JD 330 2047Z
Ref.
1920.810+- .05
978224.17
YES!!
JD 330 2055Z
Pier
1919.845+- .05


Note: Large tide variation in this port, and at the time of the measurement above it was difficult to note "C" deck height. It is only good to establish pier value.

TIME
GRAVITY
G READING
JD 331 1415Z
BGM-3
978252.06
JD 331 1415Z
KSS-30
1920.99

At 1415Z "C" deck was 1.52 m BELOW pier.
"C" deck is 5.5 m above gravity meter.
Difference between pier and gravity lab: 5.5 + 1.52 = 7.02 m

Lacoste difference in LR units:
delta_LR = pier_LR - ref_LR
-1.03 = 1919.84 - 1920.81

Difference in mGals: ( 1 LR unit = 1.0690 mGals )
delta_mgal = delta_LR x constant
-1.1 = -1.03 x 1.0690

Pier gravity value in mGals: rev_val = G + 13.6 if IT IS Potsdam corrected.
pier_grv_val = ref_val + delta_mgal + 13.6
978236.67 = 978224.17 + (-1.1) + 13.6

Height correction:
Height correction in mGals:
note: free-air constant of +0.31 mGals per meter going towards
the center of earth; -0.31 mGals per meter going away.
hgt_corr = hgt x constant
2.18 mGals = 7.02 x 0.31 mGals/m

Gravity at gravity meter level in mGals:
grv_at_meter_level = pier_grv_val + hgt_corr
978238.85 = 978236.67 + 2.18

KSS-30:

KSS_grav_val = kss_unbiased_output + bias
978249.3 = -1920.99 + 980170.29

Mistie in mGals:
mistie = KSS_grv_val - grv_at_meter_level
10.45 = 978249.3 - 978238.85

Drift in mGals since last tie:
prev_mistie: 11.31 mGals on date Oct. 23, 1994 (JD 296)

drift = mistie - prev_mistie
-0.86 = 10.45 - 11.31

==> DC Shift = prev_mistie - bias
= 11.31 - 980170.29
= -980158.98 mGals
Drift/Day = drift / (tot. # of day)
= -0.86 / (331-296) = -0.02457 mGals/day

BGM-3:

BGM_filt_grv = ( scale factor x counts ) + bias = 979537.0
using s.f. 5.0940744 and bias 8526800.
The count was filtered with a 60 filter width, run thru filter1d -FG480, and s_bgm

Mistie in mGals:
mistie = BGM_grv_val - grv_at_meter_level
13.21 = 978252.06 - 978238.85

Drift in mGals since last tie:
prev_mistie: 12.02 mGals on date Oct. 23, 1994 (JD 296)
drift = mistie - prev_mistie
1.19 = 13.21 - 12.02

==> DC Shift

Drift/Day

= prev_mistie
= 12.02
= drift / (tot. # of day)
= 1.19/ (331-296) = 0.034 mgals/day