天然和人为地震活动性的对比研究

为了充分发挥现有的区域性、地方性数字地震台站在防震减灾中的作用，中国地震局地球物理研究所与美国达拉斯南卫理大学地球科学系合作开展“中美合作延庆一怀来盆地和海城地区天然和人为地震活动性的对比研究”。该合作项目以北京西北的延庆一怀来盆地与东北辽宁的海城地区作为流动地震观测试验场，计划在现有台网的基础上，在近震源与区域性的距离上布设15套由STS—2型宽频带数字地震仪组成的流动地震台网加密观测，以改善在区域性距离上台距过长、不利于分析、解释、研究所观测到地震记录的状况。2002年秋，双方在河北怀来一带首先架设了5个宽频带数字地震台并随即投入观测。到2003年3月上旬，中方又在预定地点架设了另5个宽频带数字地震台。目前，已建成的10个宽频带数字地震台仪器运行正常，运用已获得的研究区内天然和人为地震的高质量记录，合作双方按照计划开展了相关的研究工作。     

Contrasting effects of managed opening regimes on water quality in two intermittently closed and open coastal lakes

Intermittently closed and open lakes and lagoons (ICOLLs) are shallow barrier lakes which are intermittently connected to the sea and experience saline intrusions. Many ICOLLs are mechanically opened to prevent flooding of surrounding agricultural and urban land and to flush water of poor quality. In this study, the effects of modified opening regimes (frequency and duration of barrier openings and closures) on water quality and phytoplankton in two New Zealand ICOLLs were investigated over a number of opening/closure cycles. Water quality in Lake Ellesmere (Te Waihora) responded weakly to both opening and closing events, indicating that sea–ICOLL exchange did not markedly improve water quality. Conversely, water quality in Waituna Lagoon responded rapidly to barrier openings; water level decreased to near sea level within days of opening and subsequent seawater exchange resulted in rapid decreases in nitrate and chlorophyll a concentrations. The closure of Waituna Lagoon resulted in rapid rise in water level and a pulse of nitrate and phosphorus in the water column and phytoplankton chlorophyll a concentrations increased with increasing closed-period duration. Based on data on the underwater light climate and nutrient dynamics, phytoplankton in Lake Ellesmere was probably light-limited, whereas phytoplankton in Waituna Lagoon was rarely light-limited, and appeared to be predominately P-limited. The marked differences in responses of Lake Ellesmere and Waituna Lagoon to barrier openings and closures reflected differences in ICOLL water levels and morphological characteristics, which dictated the degree of tidal flushing when the barriers were open. The inter-ICOLL differences observed in this study indicate that unless the effects of ICOLL openings/closures on phytoplankton and nutrient dynamics are understood, changes to ICOLL opening regimes may have unintended consequences for the water quality and ecology of these systems.     

Reconstructing high-magnitude/low-frequency landslide events based on soil redistribution modelling and a Late-Holocene sediment record from New Zealand

A sediment record is used, in combination with shallow landslide soil redistribution and sediment-yield modelling, to reconstruct the incidence of high-magnitude/low-frequency landslide events in the upper part of a catchment and the history of a wetland in the lower part. Eleven sediment cores were obtained from a dune-impounded wetland at Te Henga, west Auckland, northern New Zealand. Sediment stratigraphy and chronology were interpreted by radiocarbon dating, foraminiferal analysis, and provisional tephrochronology. Gradual impoundment of the wetland began c. 6000 cal yr BP, coinciding with the start of a gentle sea-level fall, but complete damming and initial sedimentation did not begin until c. 1000 cal yr BP. After damming, four well-defined sediment pulses occurred and these are preserved in the form of distinct clay layers in most of the sediment cores. For interpreting the sediment pulses, a physically based landslide model was used to determine spatially distributed relative landslide hazard, applicable at the catchment scale. An empirical landslide-soil redistribution component was added and proved able to determine the volumes and spatial pattern of eroded and deposited soil material, sediment delivery ratio and the impact on total catchment sediment yield. Sediment volumes were calculated from the wetland cores and corresponding landslide scenarios are defined through back-analysis of modelled sediment yield output. In general, at least four major high-magnitude landslide events, both natural and intensified by forest clearance activities, occurred in the catchment upstream of Te Henga Wetland during the last c. 1000 years. The spatial distribution of modelled critical rainfall values for the catchment can be interpreted as an expression of shallow landslide hazard. The magnitude of the sediment pulses represented in the wetland can be back-calculated to critical rainfall thresholds representing a shallow landslide model scenario.     

Lagoon subsidence and tsunami on the West Coast of New Zealand

Sediment core and trench data from a coastal lagoon on the West Coast of the South Island, New Zealand are used to investigate evidence for co-seismic subsidence and associated tsunami inundation. Physical data are used to document a salt marsh soil buried  80 cm below the modern sediment surface that is locally covered by a gravelly sand bed. The sediment record also contains geochemical and biological (diatom and foram) evidence for abrupt changes in salinity of lagoon waters that link to subsidence, tsunami flooding and to the open versus closed state of the lagoon tidal entrance. At the local scale, these relationships allow for separation of tsunami evidence from other agents of environmental change in the lagoon. We also propose a conceptual connection between these local changes and regional drivers of landscape development, most notably major earthquakes and resultant pulses in sediment supply to the coast.     

Height structure of thermal hard x-ray sources on the sun

The height distribution of hard X-ray bremsstrahlung is predicted for dissipative thermal models, involving rapid heating of many small (tearing mode) islands near the top of a magnetic arch. Emission at low energies () originates mainly at high altitudes in the heated kernels themselves while high energy emission comes from the Maxwellian tail electrons escaping to the chromosphere.For a power-law distribution of kernel production temperatures, the ratio of high to low altitude emissions should vary as ^–2. Recent stereo occultation results (Kane et al., 1979) are consistent with this prediction for a typical size of primary dissipation kernel 10 km/(n/10¹¹) for kernel density n(cm^–3). The prediction should also prove a useful diagnostic for SMM data.However the small kernel size required to explain the weakness of the coronal emission demands the heating of 8 × 10³⁶ electrons per second to above 5 keV temperatures. This is comparable to the acceleration rate above 5 keV needed in a thick target model, so that the thermal model has little energetic advantage in this event.     

Order parameter coupling in leucite: a calorimetric study

The thermal anomalies associated with the Ia3d → I4₁/acd → I4₁/a transition sequence of phase transitions in leucite have been studied by differential scanning calorimetry and interpreted with Landau theory. Both transitions are close to the tricritical point. The coupling between the two transitions is biquadratic, and reduces the stability of the I4₁/a phase.