U.S.S. San Francisco preparing to dock at Apra Harbor
posted Jan 10, 2005.
We have this:
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To: BigSkyFreeper
I've heard of flying into a mountain -- but not doing so underwater...
The crazy thing about the topography of the ocean floor in that area is that the seamounts of the Caroline Ridge (which the sub supposedly hit) are very near to the Marianas Trench -- the deepest spot on Earth...
My guess is that our undersea topographic mapping in this area is not too good.
3 posted on 01/09/2005 11:43:10 PM PST by TXnMA (Attention, ACLU: There is no constitutionally protected right to NOT be offended -- Shove It!)
To: TXnMA
Found this, seems to be a very interesting area.
The Yap Trench lies on the southeastern boundary of the Philippine Sea Plate in the western Pacific (Fig. 1). The Yap Trench is one section of a continuous system of arcuate trenches. These include the Izu-Bonin, Mariana, Yap, and Palau trenches, framing the eastern boundary of the Philippine Sea Plate. The Yap Trench is in a complex tectonic region of convergence between the Philippine Sea, the Pacific, and the Caroline plates. The Yap, Palau trenches, and the Ayu Trough, which is located in the southwest of the Palau Trench, form a plate boundary between the Philippine Sea and the Caroline plates. The Yap and Palau trenches are considered to be convergent boundaries, while the Ayu Trough is thought to be a divergent boundary (Weissel and Anderson, 1978; Fujiwara et al., 1995). Models of Philippine Sea Plate motion (Ranken et al., 1984; Seno et al., 1993) indicate that the rotation pole of the Philippine Sea-Caroline plates is at the junction of the Palau Trench and Ayu Trough, near 6°N, 134°E. The rate of relative plate motion is estimated to be 0.7°/m.y., that is, 0-6 mm/yr along the Yap and Palau trenches (Seno et al., 1993). The age of the subducting West Caroline Basin of the Caroline Plate is estimated to be 35°30 Ma (Bracey, 1975; Hegarty and Weissel, 1988; Yamazaki et al., 1994), and the age of the overlying Parece Vela Basin of the Philippine Sea Plate is estimated to be 30°25 Ma (Mrozowski and Hayes, 1979).
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Introduction
The Yap Trench lies on the southeastern boundary of the Philippine Sea Plate in the western Pacific (Fig. 1). The Yap Trench is one section of a continuous system of arcuate trenches. These include the Izu-Bonin, Mariana, Yap, and Palau trenches, framing the eastern boundary of the Philippine Sea Plate. The Yap Trench is in a complex tectonic region of convergence between the Philippine Sea, the Pacific, and the Caroline plates. The Yap, Palau trenches, and the Ayu Trough, which is located in the southwest of the Palau Trench, form a plate boundary between the Philippine Sea and the Caroline plates. The Yap and Palau trenches are considered to be convergent boundaries, while the Ayu Trough is thought to be a divergent boundary (Weissel and Anderson, 1978; Fujiwara et al., 1995). Models of Philippine Sea Plate motion (Ranken et al., 1984; Seno et al., 1993) indicate that the rotation pole of the Philippine Sea-Caroline plates is at the junction of the Palau Trench and Ayu Trough, near 6°N, 134°E. The rate of relative plate motion is estimated to be 0.7°/m.y., that is, 0-6 mm/yr along the Yap and Palau trenches (Seno et al., 1993). The age of the subducting West Caroline Basin of the Caroline Plate is estimated to be 35°30 Ma (Bracey, 1975; Hegarty and Weissel, 1988; Yamazaki et al., 1994), and the age of the overlying Parece Vela Basin of the Philippine Sea Plate is estimated to be 30°25 Ma (Mrozowski and Hayes, 1979).
| Fig.1: Location map of the Yap Trench. The contour interval is 2,000 m. The box shows the survey area as shown in Fig.3. The distribution of earthquake hypocenters are represented by solid black symbols: Circles = source depth shallower than 50 km, Diamonds = 50-100 km, Crosses = deeper than 100 km. Global hypocentral data from ISC since 1980.  |
Fig.2: Bathymetric map of the circumambient regions of the Yap Trench. The contour interval is 500 m. The bathymetric data are based on the global bathymetry of ETOPO5 (NGDC, 1988). The star symbol shows the pole position of Philippine Sea - Caroline plates estimated by Seno et al. (1993). The solid black symbols show hypocentral distribution. See Figure 1 caption. |
| The length of the Yap Trench is about 700 km (Fig. 2). The trench axis elongates in a convex shape toward the southeast. An arc involving the Yap Island on the Philippine Sea Plate side forms a trench-arc system. This arc consists primarily of metamorphic rocks and lacks active volcanism (Shiraki, 1971; Hawkins and Batiza, 1977). The arc-type rocks found on the islands are no younger than Late Oligocene or Miocene. The distance between the island-arc and the trench axis is about 50 km, which is much less than that of other trench-arc systems. The Caroline Ridge, oriented in an ESE-WNW direction, intersects the trench from the east. This ridge consists of a chain of seamounts thought to be of hotspot origin (Keating et al., 1984) of less than 40 m.y. (Hegarty and Weissel, 1988). Seismicity along the trench is low. Earthquakes occur at a depth of less than 50 km, and no deep-focus earthquakes are apparent along the trench. A Wadati-Benioff zone, demonstrated by a plane of deep-focus earthquakes reflecting dynamic interaction between a subducting and an overriding plates, is thus not defined. Considering the above geological and geophysical features, the Yap Trench is controversial regarding the activity of plate subduction at present. Hawkins and Batiza (1977) and McCabe and Uyeda (1983) suggested that subduction at the Yap Trench may have suspended by collision of the Caroline Ridge. McCabe and Uyeda (1983) suggested that the Caroline Ridge collided with the Yap Trench in early Miocene, and that this collision made the volcanic activity in the Yap Arc stop, and narrowing the distance between arc and trench. In contrast, some petrological and geophysical studies suggested that subduction at the trench may still be active. Fresh volcanic rock fragments and hydrothermally affected rocks, dredged in the back-arc region, may suggest in-situ or nearby hydrothermal activity in relation to Quaternary volcanic activity (Fujioka et al., 1986). High heat flow values were observed in the back-arc region and appreciably large values of negative free-air gravity anomalies were observed along the trench axis (Nagihara et al., 1989). Large negative gravity anomaly is indicative of dynamic force exerted on crust under the trench associated with ongoing subduction of the oceanic lithosphere. Observation of micro-seismic activity in the trench area suggested that tectonic force, found in active subduction zones, acted on the crust of the trench (Sato et al., 1997). |
| Prior to our study, there were insufficient data for understanding the tectonics and geodynamics of the Yap Trench. We conducted swath bathymetry and gravity surveys of the Yap Trench aboard the R/V Yokosuka in 1993, 1994 and 1996, in combination with dive surveys of the research submersible Shinkai 6500 (Fujioka et al., 1994, 1996). We hope that our study stimulates further geological and geophysical studies in this region, focused on morphotectonic characteristics, by providing a high quality base map, and that it will provide insight into the tectonics of the Yap Trench, the Philippine Sea Plate and the circum-plates. Diagrams : |
4 posted on 01/09/2005 11:59:45 PM PST by Ernest_at_the_Beach (A Proud member of Free Republic ~~The New Face of the Fourth Estate since 1996.)
To: All
Bathymetric map of the circumambient regions of the Yap Trench. The contour interval is 500 m. The bathymetric data are based on the global bathymetry of ETOPO5 (NGDC, 1988). The star symbol shows the pole position of Philippine Sea - Caroline plates estimated by Seno et al. (1993). The solid black symbols show hypocentral distribution. See Figure 1 caption.
5 posted on 01/10/2005 12:02:16 AM PST by Ernest_at_the_Beach (A Proud member of Free Republic ~~The New Face of the Fourth Estate since 1996.)
To: All; BigSkyFreeper
Survey ship tracks in the region of the Yap Trench. The solid, gray and dashed lines show the tracks from the Y95-06, Y96-12, and Y93-03 cruises of the R/V Yokosuka, respectively. The dotted lines show the tracks of the KH92-1 cruise of the R/V Hakuho-maru. The area surveyed by Iwabuchi et al. (1990) aboard the S/V Takuyo is stippled.
Looks like this survey was concerned aout mapping the deep trench areas..
No interest in the Seamount areas.
6 posted on 01/10/2005 12:06:49 AM PST by Ernest_at_the_Beach (A Proud member of Free Republic ~~The New Face of the Fourth Estate since 1996.)