Mt. Melbourne volcano,antarctica: Evidence of seismicity related to volcanic activity     

Salvatore Gambino  Eugenio Privitera 《Pure and Applied Geophysics》1996,146(2):305-318

Characterization of the microseismic activity (M _L <2.0) has been performed at Mt. Melbourne since 1990. We recorded a group of low frequency events with common morphological characteristics, i.e., an emerging onset, an unclear second phase and a sharply dropping coda. Spectral analysis of events recorded at more than one station indicates that the seismogram characteristics and spectral content are largely due to source effects. A polarization filter applied to a set of three component data revealed a first phase made up ofP waves followed (after about 0.9–1.4 sec.) by a second phase probably composed ofSH-type waves. Particle motion analysis detected a seismic ray angle direction mainly between N70°E and N110°E and apparent angle of incidence between 35° and 48° for the first phase. The studied seismicity was localized in an area on the eastern slope of Mt. Melbourne Volcano which presents a surface temperature anomaly (Mazzarini andSalvini, 1994). We formulate two hypotheses for the type of earthquakes recorded: 1) long-period events involving active presence of magmatic fluids in the source processes; 2) or the result of fracturing processes (shear?) in a medium characterized by transition between brittle and plastic behaviors. In the latter hypothesis the superficial thermal anomaly may be a symptom of this behavior at depth and is confirmed by the lown values observed for the exponential fit in the codaQ analysis.  相似文献   

赣东北鹅湖岭组的再认识   总被引：9，自引：2，他引：7  

巫建华 《地层学杂志》1996,20(2):153-160

在分析赣东北鹅湖岭组及有关地层的地质特征、地层划分现状及产生分岐的原因的基础上,提出以岩性、岩相为划分依据,将鹅湖岭组与喷发相相对应,将其下界、上界分别置于沉积喷发相与喷发相、喷发相与喷发沉积相的相变界面上。从而将北京地质学院指定的打鼓顶组建组剖面上的"打鼓顶组"并入鹅湖岭组;将赣东北其它地区的鹅湖岭组下界由安山岩层顶界处上移至安山岩层之上灰绿色砂岩层的顶界处,将铅山一上饶一带鹅湖岭组上界下移至原鹅湖岭组上部的底界处。  相似文献   

Seismic signals in geothermal areas of active volcanism: a case study from ‘La Fossa’, Vulcano (Italy)     

Antonio Montalto 《Bulletin of Volcanology》1994,56(3):220-227

Since the last eruption (1888–1890) volcanism at Vulcano, Aeolian Archipelago, southern Tyrrhenian Sea, has taken the form of persistent fumarolic activity. The gas-vapour phases of the geothermal systems are mainly discharged within two restricted areas about 1 km apart from each other, in the northern part of the island. These areas are La Fossa crater, and the beach fumaroles of the Baia di Levante. Fluids released at the two main fumarolic fields display quite different chemical and temperature characteristics, implying different origins. The local seismicity essentially takes the form of discrete shocks of shallow origin (depth1 km) at La Fossa, usually with energy < 10¹³ ergs. They are thought to be related to the uprise of pressurized hot gases and vapours discharged at the crater fumaroles. The present investigation points to the existence of two principal categories of seismic events (called M-shocks and N-shocks). These are short events (normally < 10 s). M-type shocks are thought to be due to resonance vibrations within the interior of the volcano, probably driven by the excitation of shock-waves within cavities deeply affected by deposition and alteration of self-sealant hydrothermal minerals. N-type events display features that resemble those of volcano-tectonic earthquakes, but have no recognizable S-phases. Here they are tentatively attributed to microfracturing of rocks which have been extensively hydrothermally altered. Results of the present study permit a preliminary conceptual model of the local shallow seismic processes in the framework of geochemical modelling of fumarolic activity and geological inferences from geothermal drilling.  相似文献   

The origin of accretionary lapilli   总被引：1，自引：0，他引：1  

J. S. Gilbert  S. J. Lane 《Bulletin of Volcanology》1994,56(5):398-411

Experimental investigations in a recirculating wind tunnel of the mechanisms of formation of accretionary lapilli have demonstrated that growth is controlled by collision of liquid-coated particles, due to differences in fall velocities, and binding as a result of surface tension forces and secondary mineral growth. The liquids present on particle surfaces in eruption plumes are acid solutions stable at 100% relative humidity, from which secondary minerals, e.g. calcium sulphate and sodium chloride, precipitate prior to impact of accretionary lapilli with the ground. Concentric grain-size zones within accretionary lapilli build up due to differences in the supply of particular particle sizes during aggregate growth. Accretionary lapilli do not evolve by scavenging of particles by liquid drops followed by evaporation — a process which, in wind tunnel experiments, generates horizontally layered hemispherical aggregates. Size analysis of particles in the wind tunnel air stream and particles adhering to growing aggregates demonstrate that the aggregation coefficient is highly grain-size dependent. Theoretical simulation of accretionary lapilli growth in eruption plumes predicts maximum sizes in the range 0.7–20 mm for ash cloud thicknesses of 0.5–10 km respectively.  相似文献   

Seismic hazard of Egypt   总被引：1，自引：0，他引：1  

A. El-Sayed  R. Wahlströ;m  O. Kulhánek 《Natural Hazards》1994,10(3):247-259

Earthquake hazard parameters such as maximum expected magnitude,M _max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas.  相似文献   

Palaeolimnological studies of the eutrophication of volcanic Lake Albano (Central Italy)     

Andrea Lami  Frank Niessen  Piero Guilizzoni  Julieta Masaferro  Claudio A. Belis 《Journal of Paleolimnology》1994,10(3):181-197

We use palaeolimnological techniques to reconstruct the eutrophication history of a volcanic lake (Lake Albano, central Italy) over the past three centuries. The presence of annual varves down to the bottom of the core (c. 1700 A.D.) indicated the lack of bioturbation and likely long-term meromixis. Sedimentation rates were estimated by varve counts (calcite/diatom couplets), indicating a mean rate of 0.15 cm yr^–1. The reconstruction of eutrophication was traced using past populations of algal and photosynthetic bacteria (through their fossil pigment), and geochemistry, as well as fossil remains of chironomids. Phaeophorbidea and the red carotenoid astaxanthin were used to detect past zooplankton development.The first sign of trophic change related to human activities is datedc. 1870 A.D. From that period onward a sharp increase of authigenic CaCO₃, nitrogen, N:P ratio, and dinoxanthin, a characteristic carotenoid of Chrysophyceae and Dinophyceae, is observed.Chironomid analyses showed the near absence of a deep water fauna throughout the core length. The populations of chironomid larvae are restricted to oxygenated littoral zones. In fact, the few fossil remains found are primarily of littoral origin, representing shallow water midges that were transported to profundal waters. The reduction of total chironomid in the uppermost layers of the core is to be related to human land uses.  相似文献   

河北省唐山地区丰台—野鸡坨断裂第四纪活动性——来自¹⁴C和磁性地层年代学的证据          下载免费PDF全文

陈宏强  专少鹏  陈超  赵华平  杨瑞  何娇月  胥勤勉 《中国地质》2021,48(2):605-617

丰台—野鸡坨断裂为唐山地区主要断裂之一，西侧为鸦鸿桥凹陷，东侧为唐山凸起，断裂两侧第四系厚度之差巨大。本文依据该断层两侧钻孔对其第四纪以来活动性进行初步的探讨。通过对丰台—野鸡坨断裂上下两盘PZK14和PZK20孔磁性地层学研究，并结合钻孔岩石地层，及浅部光释光和¹⁴C测年结果，建立第四纪地层格架。结果表明：两孔底部“泥包砾”为新近纪沉积；PZK14孔下更新统底界埋深为387 m，中更新统底界埋深为114 m，上更新统底界埋深为71 m，全新统底界埋深为6 m；PZK20孔下更新统底界埋深为155 m，中更新统底界埋深为73 m，上更新统底界为36 m，无全新世地层。丰台—野鸡坨断裂活动在早更新世时表现为逐渐增强的特点，活动速率由早期的5.4 cm/ka增加到13.9 cm/ka。中更新世断裂活动基本处于停滞状态，活动速率为1.0 cm/ka。晚更新世以后，断裂重新活动，且更加剧烈，活动速率达到了54.5 cm/ka。  相似文献   

Episode 49 of the Pu'u 'O'o-Kupaianaha eruption of Kilauea volcano-breakdown of a steady-state eruptive era     

M. T. Mangan  C. C. Heliker  T. N. Mattox  J. P. Kauahikaua  R. T. Helz 《Bulletin of Volcanology》1995,57(2):127-135

The Pu'u 'O'o-Kupaianaha eruption (1983-present) is the longest lived rift eruption of either Kilauea or neighboring Mauna Loa in recorded history. The initial fissure opening in January 1983 was followed by three years of episodic fire fountaining at the Pu'u 'O'o vent on Kilauea's east rift zone 19km from the summit (episodes 4–47). These spectacular events gave way in July 1986 to five and a half years of nearcontinuous, low-level effusion from the Kupaianaha vent, 3km to the cast (episode 48). A 49th episode began in November 1991 with the opening of a new fissure between Pu'u 'O'o and Kupaianaha. this three week long outburst heralded an era of more erratic eruptive behavior characterized by the shut down of Kupaianaha in February 1992 and subsequent intermittent eruption from vents on the west flank of Pu'u 'O'o (episodes 50 and 51). The events occurring over this period are due to progressive shrinkage of the rift-zone reservoir beneath the eruption site, and had limited impact on eruption temperatures and lava composition.  相似文献   

井下记录的PP和SS震相     

乌统昱  赵惠君 《地震地磁观测与研究》1992,13(2):20-26

本文在系统分析静海台井下地震记录图的基础上,发现并解决了具有一定实际和理论意义的两个问题:其一是证明了最初误认为是干扰的“双脉冲”图形实际上均是微地震。从而指出研究静海周围地区的地震活动性应考虑微震活动问题。其二确认静海周围地区微震波形的4个主要震相是P、PP、S和SS,并对地面反射波PP和SS能够观测到的条件作了初步分析,其结果进一步说明井下地震记录较之地面记录更为“逼真”,复杂和丰富。  相似文献   

相山高位岩浆房分异机制和演化   总被引：4，自引：2，他引：2  

夏林圻  夏祖春 《岩石学报》1992,8(3):205-221,T001

  相似文献