Seismic monitoring of western Pacific typhoons

Typhoons inflict large damage to societies, but are usually difficult to monitor in close proximity in real-time without expensive instruments. Here we study the possibility of using seismic waveforms on the seafloor and on land to monitor the turning of a far away or approaching typhoon. Up to 67% of the typhoons making landfall in Taiwan come from the eastern shore, so that we deployed broadband ocean-bottom seismometers (OBSs) offshore eastern Taiwan in 2006 to study ground motion in close proximity to a typhoon. Typhoons generate ocean waves, which generate pressure signals in the water column before being transmitted to the seafloor as seismic waves and recorded by the OBSs. The ground motions on the seafloor correlate with locally increased (ocean) wave heights and wave periods, suggesting that the ground motions are mostly induced by in situ or nearby pressure fields, as shown by coherence function analyses. When a typhoon turns and changes wave-wave interaction near the source region, a new set of en echelon patterns develops which can be observed by OBSs and land stations. Similar features occur when a typhoon crosses a landmass and re-enters the ocean. The energy level ratio between the single-frequency and double-frequency microseisms also changes abruptly when the typhoon turns. These features can potentially help near real-time early warning with little cost to complement other conventional typhoon early warning methods.     

The perturbation characterization of reverberation from awind-generated bubbly ocean surface. I. Theory and a comparison ofbackscattering strength predictions with data

A joint surface roughness/volumetric perturbation scattering theory is utilized to characterize bubbly ocean surface reverberation. Backscattering strength predictions are shown to be consistent with observed reverberation phenomena such as critical wind speeds, excess levels due to volumetric scattering, and saturation     

Sea surface scattering and propagation loss: review, update, andnew predictions

Sea-surface-scattering loss estimates based on perturbation methods are reviewed. The perturbation method has been known to be quite accurate for estimating low-frequency acoustic wave scattering loss. The author compares models that are based on the perturbation methods of H.W. Marsch (1961) and F.G. Bass (1960). Predictions based on numerical integration in a complex domain are presented and compared to previous predictions     

Acoustic wave scattering from two solid boundaries at the oceanbottom: reflection loss

An acoustic wave scattering model is formulated and solved for three homogeneous layers consisting of a thin solid sediment layer sandwiched by semi-infinite water and solid basalt media. The model is applied to two cases to analyze both the physical parameters affecting reflection loss and the effects of interface roughness scattering. It is shown that effects of attenuation in the sediment layer, especially of S-waves, combine with conversion and scattering processes of the basalt interface to constitute the dominant mechanism of reflection loss, especially in the small grazing angle directions. The scattering process is found not only to produce the well-known acoustic energy loss from specular to nonspecular directions, but also to alter the conversion efficiency between P and S waves with a resulting loss or gain     

A review of intact ship stability research and criteria

An investigation on capsizing of a vessel in a seaway is of paramount importance from the point of view of safety of life at sea. The present paper analyzes the major research efforts made throughout the world regarding intact stability and the establishment of stability criteria. Attempts have been made by the authors to draw conclusions from this analysis and to provide guidelines for future research efforts in the field of intact stability of ships.     

A Study of Bispectra in Relation to the Adequacy of Wave Spectral Model

In this paper.the characteristics of laboratory wind waves under various wind speeds and wat-er depths are studied.It is found that either the real or the imaginary part of the bispectrum can be relatedto the asymmetry of the wave profile,and the bicoherence is related to the ratio of nonlinear to linear wavecomponent.Occasionally,these two categories of nonlinear index lead to opposite inferences,because eachof them has its own significance and functions.The applicability of linear wave spectral model in oceanwaves becomes questionable only when strong nonlinearity is indicated by both of these two indexes.Thelinear spectral representation of wave fields does not necessarily become inadequate as water depth de-creases,and its appropriateness can be examined through the characteristics of the bispectrum.     

西沙群岛和中沙群岛及其附近海域囊甲藻属的分类研究

囊甲藻属是广泛分布在热带和亚热带海洋的一类发光甲藻。早在1872-1876年“挑战者号”航海调查(“Challenger”Expedition)中，Murray即建立了囊甲藻属，并注意到这些囊甲藻个体能产生明显的燐光，其后的调查也多次证明本属中的大部分种类都明显发光。截至目前，在世界上已记录囊甲藻12种、2变种和1变型(包括生活史还未完全了解的种类)的形态和分布。近十年来，对本属种类的亚显微构造、生活史和分类地位等也陆续作过一些研究，但仍有不少问题需要澄清。 本文是根据1974年5-6月和1975年3-4月在我国西沙群岛、中沙群岛及其附近海域，以网目边长为64微米的浮游植物网所采得的资料进行研究的，共报告囊甲藻属5种、1变种和1变型。截至目前，国内对本属尚无报道，本文中论及的种类都是我国的首次记录。     

西藏驱龙-甲玛-邦铺铜矿集区铅同位素地球化学示踪研究

驱龙-甲玛-邦铺铜多金属矿集区是西藏冈底斯成矿带上的重要矿集区,铜资源量超过1500万吨。前人研究认为三个矿床成矿物质来源于岩浆,但未讨论不同时代、不同矿化的岩浆岩铅同位素与矿石铅同位素组成的关系,并缺乏从矿集区尺度来分析。本文通过分析已发表的矿石、岩浆岩和地层铅同位素数据,认为驱龙、甲玛、邦铺矿床矿石铅与中新世含矿斑岩铅同位素特征基本一致,区别于与成矿无关的岩浆岩铅同位素组成。空间上,从南西的驱龙,至甲玛,至北东的邦铺,成矿年龄从老到新,铅同位素演化规律明显,放射成因铅递增(矿石²⁰⁶Pb/²⁰⁴Pb平均值18.521→18.644→18.684)。这种铅同位素地球化学特征不仅指示了成矿物质来自岩浆,并可区分与成矿有关和无关的岩浆岩,同时指示了成矿期岩浆岩与成矿关系的密切程度。