Red Sea heat flow

Since 1970, the number of heat flow observations in the Red Sea has increased fivefold. A new heat flow map is presented together with a table of observations. The new data confirm that the whole of the Red Sea is associated with high heat flow. The observations within 5 km distance of the deepest water of the axial trough have a mean of 467 mWm^-2 (i.e. about eight times the world mean) and the observations from 50 to 170 km from the axial deep water have a mean of 111 mWm^-2 (i.e. about twice the world mean). The heat flow distribution is thus typical of that associated with an active spreading centre. The observations are difficult to assess and interpret in detail because of the complex sedimentary and tectonic environment. The high heat flow extends at least as far as the Red Sea coasts.     

Seismicity re-evaluation of the northern Red Sea

The Aqaba subnetwork of five vertical short-period stations of the seismological observatory of King Saud University was installed in late 1986 along the eastern side of the Gulf of Aqaba, northern Red Sea. During the first six years (1986 August to 1992 July) of the subnetwork operation, 400 microearthquakes were detected. Of these, 93 events were recorded by most of the subnet stations and were located. Their epicentres lie in the northern part of the Red Sea between latitudes 25.5 N and 27.5 N and longitudes 33.5 E and 36 E along the axial depression of the Red Sea where the large intrusions (deeps) are located. Magnitudes of the locatable events ranged from 2.1 to 4.8. Two intensive swarms of about 200 microearthquakes occurred in February and June of 1992. The February swarm is the first intensive sequence observed in the surveying area since the establishment of the KSU network. Frequency-magnitude analysis of the recorded events for the period 1986-1992 yielded 3.543 for a and 0.658 for b . These relatively higher b values (0.658) are a good indication of the crustal heterogeneity under the spreading zone of the northern Red Sea. USGS and KSU data together show 3.41 for a and 0.49 for b . This study, together with historical data, confirms that the area is very seismically active and that the activity is mainly of swarm type, and may be attributed to the subsurface magmatic activity and spreading centres that are usually associated with strike-slip and normal faulting, respectively.     

洋山港海域潮动力特征及其对工程的响应

距上海陆域外约32 km的洋山港是以小洋山岛链为基础建造的中国首个离岸式深水港口, 其港区陆域是通过封堵北岛链三个主要汊道并抛填成陆而成。大规模的封堵陆连工程改变了该海域的地形边界条件, 海域潮动力特征也随之响应。通过对洋山港海域堵汊陆连工程前后潮位及潮流实测资料的分析研究, 发现洋山港海域的潮动力特征主要表现在:海域潮波倍潮及复合潮增幅随工程的进行而增大, 潮动力表现出明显的非线性特征;海域中部发生壅水;海域潮波向驻波性质变异并于憩流时段引发环状流场。     

广东闸坡海域潮汐特征分析

分别利用闸坡验潮站1975和1978年逐时潮位资料求算各自的调和常数并进行对比,验证调和常数的稳定性.结果发现,用1年逐时潮位数据进行调和常数的求算是可信的.调和常数是否稳定决定了进一步计算的非调和常数、潮位频率分布和2小时乘高潮位频率分布的可靠性.对后两者的计算,分别采用BPF方法和统计方法加以对比,以检验BPF方法的稳定性.研究表明,在只有1年逐时潮位数据的情况下,应用BPF方法进行潮位频率分布计算和2小时乘高潮位频率计算是可行的.分析结果较好地反映了闸坡海域的潮汐特征.     

Geomagnetic secular variation and secular acceleration in the Red Sea area

Summary. Estimates of the secular variation in the Red Sea over the period 1959 to 1972 have been obtained from an analysis of marine magnetic data. A total of 318 crossings of ships' tracks were used to determine the mean secular variation for the intervals 1959–72, 1959–65 and 1965–72. The mean secular variation 1959–72 shows a marked northward increase from approximately -10 nT/yr at 13°N to +27 nT/yr at 24°N. North of this, the data suggest a small decrease to + 25 nT/yr at 27° N. These values are consistent with the secular variation recorded at the nearby geomagnetic observatory at Helwan, Egypt, but less than those predicted by the 1965 IGRF for the same period.
Comparison of the mean secular variations for 1959–65 and 1965–72 yields a rough estimate of the secular acceleration of - 1.5 nT yr⁻². Analysis of the cross-over information, corrected for the latitude dependence of the secular variation, shows a regular decrease in the secular change over the period 1959–72 at all latitudes of about -1 nTyr⁻². This secular acceleration makes a substantial contribution to the overall secular change in the Red Sea and as such must be included in the correction of magnetic data covering more than a few years.