EW9709 STACKED AND MIGRATED TRANSIT SEiSMIC REFLECTION DATA This disk is a re-migration in Aug-01. The major difference between this and the earlier disk is that the the processing has been optimized for visibility during printing. They are somewhat lower resolution than the July migration but have higher amplitudes. These data represent a combination of seismic profiles shot underway between surveys on the cruise EW9709 of the R/V Ewing. The cruise was funded to survey possible drill sites for ODP Leg 199, "a Paleogene Equatorial APC Transect". They are seismic profiles from the equator to roughly 26 degrees N in the eastern central Pacific. The data were divided to form transects roughly along seafloor crust of equal age. One transect runs primarily along 56 Ma crust, while the second runs primarily along 40 Ma crust. The 40 Ma transect goes from the equator to the Clarion Fracture Zone at about 16 deg N. The 56 Ma transect goes from the equator to about 26 deg N. It jogs to the E between the Clarion and Molokai fracture zones, and back to the west north of the Molokai fracture zone. More information about the construction of the transect can be found in the attached PDF file of Marie Knappenberger's masters thesis. The data here were checked and restacked by Mitchell Lyle in July 2001. Also included are Knappenberger's picks of Neogene seismic horizons relative to a seafloor arbitrarily set at 500 msec. These data are in tab-delimited ascii format. Most of the data were recorded while the ship was underway between survey sites at 10 knots using an 80 cubic inch water gun as the seismic source. They were recorded on the Ewing's Digicon seismic acquisition system using a 2 msec sample spacing. An analog high-cut filter at 180 Hz was in place during recording. Because of the the generally high speed along the transect, significant of noise was generated by the streamer ("streamer strum") in a window of around 15-20 Hz. For this reason I used a relatively high low cut filter on the data. The data are stacked 4-channel data, processed using the following parameters: 1) static shift to account for recording delay of 5 seconds from shot 2) NMO moveout correction using 1500 m/sec velocity 3) minimum phase band pass filter (ramp up from 20-40 Hz, ramp down from 200-400 Hz) 4) The data were then stacked using a diversity stack algorithm based on the power within a sliding gate of 100 ms. 5) removal of static and storage of 2.5 seconds of data. 6) write data SEG-Y format using 4-byte IBM floating point numbers. Data were then migrated in the following manner: 1) static shift to plus 5 seconds to bring to true depth; 2) spectral shaping (15 Hz = 0%, 30 Hz= 100%, 120 Hz = 100%, 240 Hz = 0%) and 3) memory stolt F-K migration using 1500 m/sec constant velocity and stolt stretch factor of 1. Because of the length of the transects, the data were broken up into 5 blocks. The following table lists the pertinent information about each block. Block Name # of CDP's Start lat Start long End lat End long 40B1 12230 16.115 -137.768 9.295 -135.435 40B2 22528 9.294 -135.435 0.028 -138.750 56B3 22446 26.152 -147.733 13.902 -144.062 56B2 8420 13.889 -143.734 9.789 -142.640 56B1 22919 9.788 -142.640 0.074 -138.787 Navigation, center beam depth (CBD or CBdepth in header), and time of shot have been recorded in the SEG-Y binary header in the locations in the following table. Latitude and longitude have been multiplied by 10**6 to make them integer values. Negative longitude indicates west. JD refers to the Julian day of the year (number of days since the beginning of the year). Center beam depth is the depth measured by the hydrosweep swathmapping system beneath the Ewing. It is recorded in uncorrected meters, i.e., assuming 1500 m/sec sound velocity in water. Parameter # of Bytes Byte position in header CBdepth 4R (IBM) 61 Longitude 4I 73 Latitude 4I 77 Year 2I 157 Julian Day 2I 159 Hour 2I 161 Minute 2I 163 Second 2I 165