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1.
Earthquake swarms of Mt Cameroon, West Africa 总被引：1，自引：0，他引：1
Richard U. Ubangoh Bekoa Ateba Samuel N. Ayonghe G.E. Ekodeck 《Journal of African Earth Sciences》1997,24(4):413-424
Historical and recent instrumental studies of the central region of the Cameroon Volcanic Line clearly indicate the occurrence of earthquake swarms of volcanic origin. Analyses of more than 3000 micro-earthquakes recorded between 1985 and 1992 show a well-defined seismic pattern characterised by single and swarm events with duration magnitudes between 2 and 3 at depths down to 20 km. On average, the earthquakes here occur at the rate of about 2 events every 3 days with occasional earthquake swarms, which greatly increase this number. The seismic swarms comprising felt earthquakes are shown to be sometimes preceded by, simultaneous with, or followed by swarms from Bimbia and Equatorial Guinea. Mapped epicentres of some of these swarms correspond to regions of volcanic gas emissions and are parallel to the fissures on Mt Cameroon and to the inferred direction of the underlying shear zone.The quiescent periods between swarms are seen to double each year since 1986. This observation was used to predict a major seismic swarm which occurred in 1993. The data coupled with historical data, are used to infer the involvement of a magma chamber in the generation of the earthquake swarms in the region. Since the installation of the network, no eruption has been observed on Mt Cameroon. This warrants more observation in order to study the seismicity that may precede, accompany or follow an eruption of the mountain. 相似文献
2.
D. G. Nkouathio A. Kagou Dongmo J. M. Bardintzeff P. Wandji H. Bellon A. Pouclet 《Mineralogy and Petrology》2008,94(3-4):287-303
Tombel graben and Mounts Bambouto are two volcanic fields of the typical system of alternating graben and horst structure of the Cameroon Volcanic Line. Tombel graben is a young volcanic field, whereas Mounts Bambouto horst is an old stratovolcano with calderas. Volcanic products in both settings have a signature close to that of Ocean Island Basalt implying a major role of FOZO (focal zone) component and varied contribution of depleted mantle (DMM) and enriched mantle (EM) components. The Cameroon Volcanic Line is a hot line essentially resulting from passive rifting. Eocene to Recent intraplate basaltic volcanism in the study area was probably a result of mantle upwelling coupled with lithospheric extension. The olivine basaltic magma of horst volcanoes evolved in a large-scale, steady-state magmatic reservoir via crystal fractionation and limited contamination to highly differentiated alkaline lavas (trachyte and phonolite). Conversely, rapid ascent of lavas along multiple fault lines of graben structures produced less evolved lavas (hawaiite) within small reservoirs. This model, evaluated for the study area, involves mantle upwelling inside zones of weakness in the lithosphere after intra-continental extension. It can be applied to other parts of the Cameroon Volcanic Line as well, and is similar to that described in other intra-continental rift-related areas in Africa. 相似文献
3.
Severin Nguiya Marcelin Mouzong Pemi Alain Pierre Tokam Évariste Ngatchou Heutchi Willy Lemotio 《Comptes Rendus Geoscience》2019,351(6):430-440
In this study, the recent update of the gravity database with new measurements has raised the opportunity of improving the knowledge of the crustal structure beneath the large volcanic system called Mount Cameroon, and its implication in the regional tectonics. The multi-scale wavelet analysis method was applied to highlight the geologic features of the area, and their depths were estimated using the logarithmic power spectrum method. The results reveal a complex crustal structure beneath Mount Cameroon with high variation in the lateral distribution of crustal densities. The upper and lower crusts are intruded by dense materials originating from the mantle with less lateral extension. The trends of Tiko and Ekona faults along the intrusion suggest tectonic activities as deep as 25 km. The difference in mantle composition or temperature between the East and the West of the studied area is clearly seen in detailed wavelet images and agrees with a mantle origin for the Cameroon Volcanic Line. 相似文献
4.
5.
Fulbert Mbowou Ngantche Igor Sébastien Owona Boris Chako Tchamabe Justin Lissom Bruno Lanson Emmanuel Ekodeck Georges 《中国地球化学学报》2020,39(6):830-861
Acta Geochimica - Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke... 相似文献
6.
Abstract: Mount Bambouto is a polygenic stratovolcano of the Cameroon Volcanic Line, built between 21?Ma and 4.5?Ma. It is situated approximately 200?km NE of Mount Cameroon, between 09°55′ and 10°15′ longitude east and, 05°25′ and 05°50′ latitude north. The volcano covers an area of 500?km2 and culminates at 2740?m at Mélétan dome and bears a collapsed caldera at the summit (13?×?8?km). Mount Bambouto is characterized by several natural hazards of different origins: meteorological, such as landslides and rock falls; anthropogenic, such as bushfires, tribal wars and deforestation; and volcanological, such as volcanic eruption. The thematic map shows that 55–60% of the caldera has high probability of occurrence of mass movement. The caldera has a high population density (3000 inhabitants), which increases the level of risk, evaluated at approximately $US3.8 million for patrimony, 3000 civilian deaths and destruction of biodiversity. 相似文献
7.
本文以汶川地震强震区北川县典型研究区为例,利用高分辨率航片、SPOT5卫星图像对北川县典型研究区进行了512地震之后和924降雨之后诱发的滑坡解译,解译结果显示:512地震诱发滑坡1999个,924强降雨诱发滑坡828个,924强降雨导致原有地震滑坡面积扩大的滑坡150个。研究表明:地震和强降雨都是诱发滑坡的动力成因,924强降雨诱发的滑坡面积是512地震诱发滑坡面积的1/4倍,强降雨诱发滑坡的数量增加了41.4%; 强降雨不仅诱发新的滑坡,而且促使原来地震滑坡复活,并扩大其面积,强降雨导致地震诱发的滑坡面积扩大了原面积的68.7%。同时,在遥感解译数据基础之上,开展地震诱发滑坡与降雨诱发滑坡规模对比和控制因子耦合分析及地震与降雨耦合灾害链模式研究,为进一步分析研究地震灾区滑坡的产生、发展趋势、危险性和风险评价等预测预报提供科学依据,也为汶川震区恢复重建中的减灾防灾提供决策参考。 相似文献
8.
松辽盆地昌德地区火山岩储层以酸性岩为主,主要岩石类型为熔结凝灰岩和凝灰岩,与国内其他含油气盆地的火山岩储层明显不同。宏观上岩性较致密,岩心观察仅见构造裂缝和溶蚀孔,局部见溶蚀洞,显微镜下观察储集空间类型多样,发育粒内溶孔、晶内熔孔、晶间微孔、构造微裂缝、炸裂缝和收缩缝等。火山岩厚度普遍较薄,其中芳深9井区火山岩厚度最大,最厚仅为75m。从岩相类型看,芳深9井附近为爆发相,其他地区为溢流相。研究区火山岩为低孔低渗储层,岩性和岩相与物性关系密切,同时控制着原生孔隙的形成。后期的成岩改造,包括构造活动、溶蚀作用等决定了次生孔隙的发育程度,构造运动产生的裂缝是该区储层得以改善的主要因素,而后期充填作用破坏了储层的储集性能。火山口附近爆发相与溢流相的叠合区是天然气勘探的有利目标。 相似文献
9.
琼北火山活动分期与全新世岩浆演化 总被引：12，自引：9，他引：12
琼北火山活动始于始新世以来，早第三纪火山岩以夹层隐伏于不同时期的地层中。本文新提供的琼北火山岩K-AT年龄和砂岩捕虏体热释光年龄，从年代学上确定了琼北存在全新世火山喷发活动。琼北地表火山岩从早到晚分为6期：蓬莱期(中新世)、金牛岭期(上新世)、多文岭期(早更新世)、东英期(中更新世)、道堂期(晚更新世)、雷虎岭期(全新世)。雷虎岭期又分为早晚两个亚期：雷虎岭亚期和马鞍岭亚期，它们分别属于橄榄拉斑玄武岩和石英拉斑玄武岩。火山岩稀土元素、微量元素和Sr，Nd，Pb同位素地球化学特征揭示，岩浆来自亏损地幔(DMM)和富集岩石圈或亏损地幔(DMM)与俯冲洋壳两种不同的地球化学组分混合源区。橄榄拉斑玄武岩是相对原始的地幔岩浆。橄榄拉斑玄武岩岩浆经约10％橄榄石分离结晶可以形成石英拉斑玄武岩浆。岩浆上升过程中未受明显的陆壳混染。 相似文献
10.
Scientific visits to Lake Nyos in Northwestern Cameroon in the aftermath of the gas disaster that killed over 1,750 people in 1986 revealed the presence of a pyroclastic natural dam in the northern border of the lake. This dam is being affected by back erosion. Collapse of the dam could cause a flood that would affect inhabited areas over a 220?km distance. Timing of dam collapse has been hotly debated based on vastly different carbon-14 and potassium-argon formation ages. In previous work, we used uranium series disequilibria to suggest a formation age of >5,000?years. Detailed comparison of uranium series and trace element data for lavas of Lake Nyos and Mt. Cameroon, both belonging to the Cameroon Volcanic Line, suggests that Lake Nyos basalts erupted with an initial radium-226/thorium-230 ratio that is two times higher than lavas erupting on Mt. Cameroon today. This information is used to infer an age of 8,750?±?490?years, which we suggest is the formation age of the Lake Nyos dam. The erosion rate deduced from this age does not indicate that collapse of the dam from back erosion alone and the attendant potential flood disaster are as eminent and alarming as previously thought. However, other factors militate for action to secure the dam. Work is underway to reinforce it by engineering methods. 相似文献
11.
石灰石矿山采场崩塌是藏东昌都地区常见的地质灾害类型,是矿山企业安全生产和铁路工程建设面临的主要地质安全问题之一。文章采用基础地质、构造地质和灾害地质相结合的方法,通过详实的地质灾害调查,查明崩塌发育规律,分析岩体结构面特征,探讨崩塌灾害的形成机理,并建立其破坏模式。结果表明：藏东昌都地区上三叠统石灰石矿山采场崩塌沿区内褶冲带呈线状展布;岩体内发育纵张节理(S1)、横张节理(S2)、“X”型共轭剪节理(S3、S4)及层间剪节理(S5)共5组与区域褶皱和对冲系断裂配套的陡倾构造结构面,将岩体切割为破碎的块体;研究区崩塌地质灾害是内、外动力地质作用耦合的产物。晚三叠世(T3)早期,昌都地区陆内裂谷盆地环境沉积形成的上三叠统波里拉组(T3b)灰岩是崩塌发育的沉积建造基础;新生代(Cz)印度-欧亚大陆碰撞引发的强烈褶皱造山运动奠定了区内构造格架,是崩塌发育的必要条件;第四纪(Q)以来的强烈新构造运动和晚更新世(Q3)以来的... 相似文献
12.
火山喷发过程所伴生的地震活动会诱发大量的崩塌滑坡次生灾害,其所造成的人员财产损失甚至超过火山活动本身。2002年以来长白山天池火山区地震活动的异常,表明火山深部的岩浆正在发生变化,天池火山存在喷发的危险。地震崩塌滑坡的危险性区划是降低生命财产损失的有效手段。将火山伴生地震作为崩塌滑坡灾害的诱发因素并据此设置地震参数,利用简化的Newmark累积位移模型,考虑地形因素对地震的放大效应,对长白山地区天池火山喷发下次生崩塌、滑坡灾害的危险性进行评价。通过探讨不同地震震级下的危险性分区结果,认为不同地震参数的设置对危险性分区结果没有影响。将研究区划分为极高、高、中等、低、极低等5个危险等级,其中,极高危险区主要分布在3个区域:以天池口为中心,40km为半径的范围内;沿江乡—两江镇—松江镇条带区域;长白县境内鸭绿江沿岸区域。 相似文献
13.
长岭断陷深层火山岩大量发育,储集空间类型丰富,有利储层发育。将火山岩储层的形成分为2个主要阶段,即初始成岩阶段和成岩后生阶段。初始成岩阶段形成原生孔隙,成岩后生阶段形成次生孔隙。火山岩在初始成岩阶段和成岩后生阶段都可以形成大量的各种规格的裂缝,不同阶段的裂缝具有不同的形成机制和不同的特点,这些裂缝是火山岩地层能作为储层的关键所在。火山机构横向并列叠置,火山岩厚度大,呈多旋回发育的特征,是深层主要的储层。盆地深层广泛发育的厚层火山岩储层与烃源岩、深大断裂配置,形成有利的勘探目标,勘探潜力巨大。 相似文献
14.
During the 2008 Wenchuan earthquake, the river valley from Yingxiu to Wenchuan experienced numerous landslides and became a prominent area of landslide complexes. The present large landslide complex near the earthquake epicenter consisted of Laohuzui slide 1, Laohuzui slide 2 and Douyaping slide. The scale, geology, morphology, sliding process, and failure mechanism of the landslide complex are analyzed by means of field investigation, aerial photograph and stereographic projection technique. Characteristics of these three slides including seismic response of slope, landslide debris, damage and potential failure are discussed: the convex slope and the upslope of fractured granitic rock at high altitude are highly prone to landsliding under earthquake; the high source altitude and long travel path determine grain sizes and the deposit angle of the slide debris; the landslide complex completely buries the G213 roadway and dams up the Minjiang River in these sections; after the earthquake, rainfall, aftershocks and river erosion may retrigger new failures, such as retrogressive slide of weathered fractured rock, colluvial landslide, debris flow, embankment failure and rockfall. The following are presented as suggested remedial measures to protect the roadway and stabilize the slope: the removing and trenching, protective concrete/rock blocks against erosion, retaining structure, rockfall stopping wall, rockfall restraining net, rock bolt, and the planting of vegetation. 相似文献
15.
甘肃西部及邻区铀矿化特征和找矿方向 总被引：5，自引：0，他引：5
区内铀矿床分为6种类型:伟晶状白岗岩型、钠交代岩型、花岗岩型、火山岩型、碳硅泥岩型和砂岩型。本区铀矿主成矿期为海西期,其次为燕山期和中条期。矿床、矿点主要集中分布于冷龙岭、龙首山、潮水等6条成矿带。铀成矿主要受裂谷带及与之相邻的拱断带、夹持于花岗岩带之间的中新生代盆地、富碱的酸性侵入岩和火山岩、断裂构造、沉积相、氧化还原分带等因素的控制。潮水盆地、雅布赖盆地、巴丹吉林盆地等是找矿的主要远景区。 相似文献
16.
2010年玉树7.1级地震诱发滑坡特征及其地震地质意义 总被引：3，自引：0，他引：3
2010年玉树7.1级地震造成了一系列次生地质灾害。笔者在玉树灾区地震地质灾害调查基础上,结合Quickbird高分辨率遥感影像数据和航片影像数据,以目视解译为主,共提取了542处地震滑坡,并首次发现了11处古地震滑坡。调查研究结果显示,玉树地震滑坡主要包括崩塌、狭义的滑坡和土溜等三种类型。其中地震崩塌占到了90%以上,按其物质成分可进一步划分为碎屑型崩塌、碎屑流型崩塌和岩崩等三类。地震滑坡的空间展布特征显示,该区80%以上的地震滑坡集中分布在以玉树活动断层为轴的长约95km、两侧宽2km的廊带区内,并与发震断层距离和宏观震中有很好的相关性,其高密度区与同震地表破裂的空间分段性也有很好的对应关系,体现出典型的走滑型发震断层的控灾特点。同时,还进一步分析了山体坡度、坡体形态、临空面高度和地层岩石与岩体完整度等因素对地震滑坡总体分布的影响。对古地震滑坡的初步研究发现,古地震滑坡的规模、期次和分布特征间接地反映出玉树断裂带在全新世期间曾发生过多次震级强度明显大于本次玉树7.1级地震的古地震事件,这为更深入探索玉树断裂带古地震事件提供了另一种重要的研究途径。此外,地震滑坡分布与地表破裂和极震区破坏程度之间的密切空间关系指示,地震滑坡也可以成为快速圈定宏观震中以及开展极震区地震烈度评价等方面的重要指标。 相似文献
17.
Tiabou Anicet Feudjio Temdjim Robert Wandji Pierre Bardintzeff Jacques-Marie Che Vivian Bih Bate Tibang Edith Ekatah Ngwa Caroline Neh Mebara François Xavier Onana 《中国地球化学学报》2019,38(1):40-67
Acta Geochimica - Three monogenetic cones in the Baossi–Warack area, Ngaoundéré, Adamawa Plateau forming part of the Cameroon Volcanic Line (CVL) are documented in this study.... 相似文献
18.
Gerassimos A. Papadopoulos 《地学学报》1993,5(4):399-404
The earthquake (Ms= 5.3) of 20 March 1992 and its aftershocks, which occurred near the volcanic island complex of Milos, South Aegean, Greece, are studied on the basis of filed observations and instrumental data. The mainshock caused some building damage, the maximum intensity of VI+ (MM) being assigned to Triovasalos, Milos. Ground cracks, liquefaction in soil, landslides and rockfalls were observed in Milos. Liquefaction took place at an apparently anomalously long epicentral distance (D= 12 km) and is associated with unusually small earthquake magnitude. Abnormal animal behaviour was reported no longer than twelve hours before the mainshock. The b-value (= 1.02) of the G–R relation for the aftershock sequence, the exponentially decreasing number of aftershocks with time, and the difference (= 0.5) in magnitude between the mainshock and its largest aftershock imply that the origin of these earthquakes is tectonic and not associated with the volcanic field of Milos. 相似文献
19.
《Comptes Rendus Geoscience》2018,350(3):100-109
We investigated mafic and felsic volcanic rocks from the Bamoun plateau, a magmatic province located north of Mount Cameroon, in the continental part of the Cameroon Volcanic Line (CVL). Basalts and dacites were probably emplaced more than 40 Ma ago, while basanites represent very young volcanic eruptions. Among the basalts, some of them have suffered crustal contamination during their uprise through the continental crust, and their primary trace element and isotopic compositions have been slightly modified. The formation of the dacites was also accompanied by some crustal contamination. Non-contaminated rocks show that the oldest magmas are transitional basalts formed by relatively high degrees of partial melting of a moderately enriched mantle source, probably containing pyroxenites. Recent basanites were produced by very low partial melting degrees of an enriched mantle source with HIMU composition, but different from the source of the nearby Mount Cameroon lavas. The mantle beneath the CVL is thus very heterogeneous, and the tendency towards more alkaline mafic-ultramafic compositions in the youngest volcanic manifestations along the CVL seems to be a general feature of all CVL. 相似文献
20.
准噶尔盆地火山岩油气勘探取得重大进展。笔者经综合研究,提出影响该区天然气藏形成的石油地质主要特征是：前陆坳陷控制了烃源岩区域展布,后碰撞火山岩是主要的储层,古生代晚期的构造优化了储层物性并形成圈闭。松喀尔苏组为前陆坳陷磨拉石建造的近端粗碎屑岩沉积,是克拉美丽造山事件后快速沉积产物,作为主要烃源岩的下石炭统滴水泉组,是与松喀尔苏组同期前陆坳陷不同位置的沉积层系,滴水泉组是前陆坳陷中央的细粒沉积层系。后碰撞火山岩覆盖在前陆坳陷沉积层系之上,分布广泛,分布范围不受古生代造山带和现今构造单元控制。二叠纪发育断陷构造,形成凹隆相间的构造格局,在构造高部位的隆起区石炭系火山岩风化壳和构造裂缝,优化改善了火山岩储层的储集性能,形成有利油气运移通道和储集空间。克拉美丽山南缘的前陆坳陷中央为有利烃源岩分布区,该范围内的构造高部位的火山岩发育区,将是准噶尔盆地东部下一步火山岩油气藏勘探的有利区域。 相似文献