报告一：
题目：Advanced geophysicalstudies of accretion of oceanic lithospherein Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings
报告人：徐敏 博士 毕业于美国麻省理工学院-伍兹霍尔海洋研究所联合研究生项目（MIT-WHOI Joint Program）
地点：海洋楼215会议室
时间：2012年7月6日（周五）14:00
报告人简介：徐敏 博士 毕业于美国麻省理工学院-伍兹霍尔海洋研究所联合研究生项目。主要研究兴趣为海洋岩石圈的形成、大洋中脊的地震结构、热液喷口系统、地震层析成像等。
报告摘要：The structure of the oceanic lithosphere results from magmatic and extensional processes taking place at mid-ocean ridges (MORs). The temporal and spatial scales of the variability of these two processes control the degree of heterogeneity of the oceanic lithosphere, represented by two end-member models: the classical Penrose Model exemplified by layered magmatic crust formed along fast-spreading MORs, e.g., East Pacific Rise (EPR); and the recently defined Chapman Model describing heterogeneous mafic and ultramafic lithosphere formed in settings of oceanic detachment faulting common along slow-spreading MORs, e.g., Mid-Atlantic Ridge (MAR). This study is using advanced marine geophysical methods (including finite-difference wave propagation modeling, 3D multi-channel seismic reflection imaging, waveform inversion, streamer tomography) to study lithospheric accretion processes in MORs characterized by contrasting tectono-magmatic settings: the magmatically dominated EPR axis between 9°30'-10°00’N, and the Kane Oceanic Core Complex (KOCC), a section of MAR lithosphere (23°20’-23°38’N) formed by detachment faulting. At the EPR study area, I found that the axial magma chamber (AMC) melt sill is segmented into four prominent 2-4-km-long sections spaced every ~5-10 km along the ridge axis characterized by high melt content (>95%). In contrast, within the intervening sections, the AMC sill has a lower melt content (41-46%). The total magma volume extracted from the AMC sill was estimated of ~46 __MCE_ITEM____MCE_ITEM__´ 106 m3, with ~24 __MCE_ITEM____MCE_ITEM__´ 106 m3 left unerupted in the upper crust as dikes after 2005-06 seafloor lava eruption. At the KOCC, I used streamer tomography to constrain the shallow seismic velocity structure. Lithological interpretation of the seismic tomographic models provides insights into the temporal and spatial evolution of the melt supply at the spreading axis as the KOCC formed and evolved.
报告二：
题 目：Post-seismic deformation and stress changes following the 1960 M9.5 Valdivia Chile earthquake: Implications for its relationship with the 2010 M8.8 Offshore Bio-Bio, Chile earthquake（1960年9.5级智利大地震的震后形变和应力变化以及与2010年8.8级大地震的关系）报告人：丁忞 美国麻省理工学院-伍兹霍尔海洋研究所联合研究生项目（MIT-WHOI Joint Program）研究生三年级
地点：海洋楼215会议室
时间：2012年7月6日（周五）15:00
报告人背景：丁忞美国麻省理工学院-伍兹霍尔海洋研究所联合研究生项目研究生三年级。主要研究兴趣为俯冲带的岩石圈结构及火星火山结构。
报告摘要：We analyze the post-seismic viscoelastic deformation and the associated Coulomb stress changes following the 22 May 1960 M9.5 Valdivia, Chile earthquake, focusing on its relationship with the 27 Feb. 2010 M8.8 offshore Bio-Bio, Chile earthquake. We demonstrated that post-seismic viscoelastic mechanism can provide an alternative mechanism to the co-seismic after-slip model [Barrientos and Ward, 1990], adequately explaining the observed land level changes along the Chile Central Valley leveling line in 1960-1964 and around the Corcovado Gulf in 1960-1968. We found that the regional viscosity model with a lithosphere thickness of 60-70 km, an asthenosphere Maxwell decay time of 1.25-5.0 yr, and an asthenosphere thickness of 100 km, can yield results that are consistent with those observations. Our calculations also revealed that viscoelastic creep of the asthenosphere have caused Coulomb stress increase of 0.5-1.5 bar at the 2010 epicenter, which is larger than the Coulomb stress increase of 0.4 bar estimated by the after-slip model [Barrientos and Ward, 1990]. The viscoelastic stress change is of the same order of magnitude as the co-seismic stress changes caused by five M>7.6 earthquakes during 1835-2010 at the Darwin gap. While the 2010 rupture slip distribution appears to be controlled primarily by the spatial pattern of the coupling coefficient of the fault plane, viscoelastic deformation might have played a potentially significant role in triggering the earthquake.
学术报告3：Crustal structure and supporting mechanisms of topography on Mars
报告人：丁忞美国麻省理工学院-伍兹霍尔海洋研究所联合研究生项目（MIT-WHOI Joint Program）研究生三年级
地点：海洋楼215会议室
时间：2012年7月6日（周五）15:30
报告摘要：The Mars gravity model to the spherical harmonic degree of 85 with a resolution of ~70 degree was previously used to determine the crustal structure of Mars [Neumann et al., 2004]. We updated the Mars crustal model to a higher resolution, including additional data from the MRO and Mars Odyssey missions through October 2008 and a new gravity model MRO110B2 delivered by JPL, which has a higher special resolution to the degree of 110 with a resolution of ~90 degree. We inverted the crustal thickness models, using two end-member downward continuation filters and assuming crustal density of 2.8-3.1 g/cm3 and mantle density of 3.5 g/cm3. We show that the inverted crustal thickness model has a spatial resolution ~ 200 km, which is improved over previous models. For the crustal thickness model using crustal density of 2.9 g/cm3 and minimum amplitude downward continuation filter, we compare the modeling results with the Airy-Heiskanen model to investigate the isostatic support of the topographic highs in the Tharsis Province and topographic lows in several impact basins. We found that the Tharsis Province, which is characterized by elevated topography, is generally in isostatic state for the early volcanic constructions. Within the Tharsis Province, local positive Bouguer anomaly and the corresponding uplifted Moho shape of the Tharsis Mons, Olympus Mons, and Alba Patera are inferred to be associated with crust thinning or igneous intrusion. For the large impact basins where the crust is isostatically compensated, positive Bouguer anomaly and thinned crust are associated with crater processes. In comparison, some mascon basins with large Bouguer anomaly are thought to be associated with super-isostatic processes. In Terra Sirenum, Arabia Terra, and Noachis Terra, where magnetic stripes are observed, the topography is generally in the state of isostatic compensation, suggesting that those terrains formed during the early stage of Mars evolution. This interpretation is consistent with the hypothesis that the core convection dynamo, which formed the Mars magnetic field, exists in Noachian [Connerney et al., 1999].
最后更新 (2012-09-28 10:21)