Celebes Sea Research Articles

Terrestrial heat flow in the Celebes and Sulu Seas

Five heat flow measurements were made in the Asiatic Mediterranean Sea; two in the Celebes Sea and three in the Sulu Sea. The mean of all five values of 2.0 μcal/cm2 sec is significantly greater than the over-all mean heat flow value for the oceans and is close to the mean value for marginal seas. The measurement indicate that there may be a difference in the flow of heat through the two seas.

Earthquake mechanisms and island arc tectonics in the Indonesian-Philippine region

abstract Forty-four new focal mechanisms from shallow-focus earthquakes in the Indonesian-Philippine region have been determined from P and S waves recorded on long-period instruments. The dominant modes of deformation are thrust and normal faulting rather than strike-slip faulting. Along the Sunda and Philippine arcs the most active zone of shallow focus activity occurs between the ocean trench and the line of active volcanoes. Mechanism solutions from earthquakes in this zone are all of the thrust type with the sense of motion on the shallower dipping of the two nodal planes consistent with underthrusting beneath the island arc. Seismic slip vectors strike in a northeasterly direction along the convex side of the western Sunda arc and strike in a westerly direction along the Philippine arc and its extension along the eastern margin of the Celebes Sea. Normal faulting mechanisms from one earthquake under the Java Trench and another under the Philippine Trench may result from extension in the upper surface of the lithosphere as it bends beneath the island arc. The curvature of the Sunda arc may have caused the inclined seismic zone beneath the arc to shoal toward the northwest. There is a correlation between negative isostatic gravity anomalies, maximum water depth in the trench and the length and shape of the seismic zone beneath the Sunda arc. Shoaling of the inclined seismic zone beneath the nearly linear Phillippine arc can be explained by a decrease in the slip rates from south to north along the arc. Complex regions such as western New Guinea, the Sulu Spur and lesser Philippine islands may include a number of small plates of lithosphere.

Earthquakes during March

AT least eleven strong earthquakes occurred in the world during March. The greatest, and also the ed on March 4 from a focus having near lat. 36-5° N., long. 70-5° E., in the ush, Afghanistan. The depth of focus was probably rather greater than 200 km. and the strength 7½ on the instrumental scale. Owing to its strength and depth, the shock was felt over a wide area in Afghanistan and the North -West Frontier Province, Pakistan, and although the full extent of the damage is not yet assessed, the earthquake is known to have damaged the Roman Catholic cathedral in Lahore. The next most intense (scale c. 7) was probably that occurring on March 27 from a focus having an epicentre in the Celebes Sea off the southern coast of Cape Mindanoa. Strong shocks on March 16 and 17 had their epicentres in the region of the Bismarck Archipelago. On March 9 an earthquake with strength 5½ and epicentre near lat. 37–1° S., long. 121-3° W., in central California set off burglar alarms and rolled stones off Telegraph Hill, San Francisco, but did no serious damage. At Hollister some windows and plaster were cracked, and small objects were shaken off shelves. Of the small shocks during the month, three may be mentioned. On March 7 an earthquake was felt with strength 3–4 on the Modified Mercalli scale in the south-west Alps near Messtetten. It had a depth of focus, according to Dr. W. Hiller, of Stuttgart, of less than 5 km. On March 11 a strong tremor shook the area around Dalton, New South Wales, Australia, and cracked buildings there, causing damage estimated at £2,000. The shock was felt in Sydney and Canberra. On March 22 an earthquake was felt in the Departement des Basses-Alpes, France, doing some damage at Lauzet. Instrumental readings for the month have been received from the central stations of the United States Coast and Geodetic Survey in co-operation with Science Service and the Jesuit Seismological Association ; the Central Seismo-logical Bureau at Strasbourg ; and individual observatories at De Bilt (Netherlands), Durham, Stuttgart and Toledo.

Earthquakes during June

DURING June there occurred at least nine world-shaking earthquakes and a great number of smaller ones. The greatest two of the month were that on June 28, which caused heavy casualties and severe property damage in and around Fukui, West Honshu, Japan (Nature, July 10, p. 57) and which gave ground amplitudes at Durham of 115µ, and that on June 30, which caused casualties and property damage on the island of Levkas and the nearby mainland of Greece, and gave ground amplitudes of 220µ at Kew. The other great shocks were on June 15 near the southern coast of Honshu, Japan ; on June 18 in the Solomon Islands region ; on June 21 in the Celebes Sea ; on June 27 (2) off the northern coast of Honduras and south of the Alaska Peninsula ; and on June 29 (2) in the Samoan Islands region and in Transcaucasia. An earthquake only slightly less intense occurred on June 13 from a focus the epicentre of which was near lat. 43°31‘N., long. 12° 8‘E. This caused some property damage and at least one death at San Sepolcro in the Italian Province of Arezzo. Also during the month there was a swarm of earthquakes in the Karlsruhe, Rasstat, Lauterbourg area. The swarm began on June 1 and lasted practically the whole month, the greatest shock of the series being felt on June 7 with scale VI to VII (some chimneys down) at Karlsruhe. The epicentre of this shock was near lat. 49°04‘N., long. 8°19‘E. some 9 km. north-west of Karlsruhe, and the depth of focus has been estimated at 20–30 km. The energy of the shocks of this swarm did not travel far, but was recorded by the seismographs at Strasbourg, Stuttgart and the Swiss observatories. Apart from the observatories mentioned above, reports for the month have also been received from the U.S. Coast and Geodetic Survey, Aberdeen, Beograd, Cleveland (Ohio), De Bilt, Toledo and Uccle.

The Castration of the Domestic Animals.

The Sulu Sea is a semi-isolated, marginal basin surrounded by high sills that greatly reduce water inflow at mesopelagic depths. For this reason, the entire water column below 400 m is stable and homogeneous with respect to salinity (ca. 34.00) and temperature (ca. 10 °C). The neighbouring Celebes Sea is more open, and highly influenced by Pacific waters at comparable depths. The abundance, diversity, and community structure of pelagic cnidarians was investigated in both seas in February 2000. Cnidarian abundance was similar in both sampling locations, but species diversity was lower in the Sulu Sea, especially at mesopelagic depths. At the surface, the cnidarian community was similar in both marginal seas, but, at depth, community structure was dependent first on sampling location and then on depth within each Sea. Cnidarians showed different patterns of dominance at the two sampling locations, with Sulu Sea communities often dominated by species that are rare elsewhere in the Indo-Pacific. Mesopelagic and bathypelagic species recorded in the Sulu Sea did not have significantly different vertical distributions in the Celebes Sea. However, some deep mesopelagic genera were absent from the Sulu Sea in the sampled depth range. These results suggest that a combination of environmental and physiological parameters determine the distribution and dominance of pelagic cnidarians.