Gravity and seismicity analyses of the El Chichon volcano,Chiapas, Mexico     

F. Medina  T. Gonzalez-Moran  L. Gonzalez 《Pure and Applied Geophysics》1990,133(1):149-165

Subduction induced compressional stress, lateral displacement faults probably linked to the NW extension of the Polochic-Motagua fault system, and local magma emplacement create a complex geological setting for the El Chichon volcano.Gravity analysis reveals that the principal structures in the area correspond to synclines and anticlines. Downward continuation of the gravity field suggests the presence of magma emplacement SE of the volcano. This magmatic emplacement appears to be the principal cause of the truncation of the syncline in which the volcano lies.Analyses of earthquakes occurring after eruptions show that the vertical distribution of events is confined to a roughly cylindrical zone which correlates well with the region of magmatic emplacement inferred from the gravity analysis.Even though more than 350 km separate the volcano from the Middle American trench, the compressional stress regime reported for the area may correlate with subduction stress (N30°E). However, the strike direction for the principal faults in the zone, N60°W, permits us to postulate that the NW extension of the Polochic-Motagua fault system is implicated in the local tectonics of the El Chichon area.  相似文献   

A local landscape in transition between production and consumption goals: can new management arrangements preserve the local landscape character?     

Teresa Pinto-Correia  Mara Almeida  Carla Gonzalez 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2016,116(1):33-43

Around towns in the Alentejo region, the landscape is dominated by a characteristic agricultural small-scale mosaic. These areas are central in the region landscape character – even if the large-scale latifundia landscape of the extensive silvo-pastoral systems is most commonly associated with the region. In the last two decades, these parcels became extremely attractive for new comers, who settle in the rural context as residents, week-end visitors, being often also lifestyle farmers. The paper presents a case study landscape, in Montemor-o-Novo, a small town 100 km from Lisbon, highly subject to the pressure for consumption uses, by urban users. The study shows that the new owners, even if they have settled in the area due to the tranquility and social bindings of the rural, end up doing farming, with new or reshaped production objectives, markets and models, but at the same time maintaining the traditional farm systems. Thus, the landscape character is maintained, so far. Nevertheless, the role of these neo-rurals and lifestyle farmers is still an unseen role, both by the agriculture and the planning sectors. And thus the question is, whether the combination of actors and land management drivers will continue maintaining the landscape in the future.  相似文献   

Paleoearthquake evidence in Tenerife (Canary Islands) and possible seismotectonic sources     

L. I. Gonzalez de Vallejo  R. Capote  L. Cabrera  J. M. Insua  J. Acosta 《Marine Geophysical Researches》2003,24(1-2):149-160

A series of clastic dikes and tubular vents were identified in southern Tenerife (Canary Islands). These features are the result of seismic liquefaction of a Holocene sand deposit, as the consequence of a high intensity paleoearthquake. The peak ground acceleration (pga) and magnitude of the paleoearthquake generating these liquefaction features were estimated by back calculation analysis. A representative value of 0.30 ± 0.05 g was obtained for the pga. From this, an earthquake intensity of IX was estimated for the liquefaction site. Magnitude bound methods and energy based approaches were used to determine the magnitude of the paleoearthquake, providing a moment magnitude M = 6.8. The zone in which the liquefaction structures are found has undergone tectonic uplift and is affected by two faults. One of these faults was responsible for displacing Holocene materials. Dating of the uplifted sand formation indicates an age of 10,081 ± 933 years, the liquefaction features ranging from this age to 3490 ± 473 years BP. This paleoearthquake was of much greater magnitude than those known historically. Faults with neotectonic activity are significant features that should be borne in mind when assessing the seismic hazards of the Canary Islands, presently considered as low and mainly of volcanic origin.  相似文献   

The coast of Mexico: approaches for its management     

Evelia Rivera-Arriaga  Guillermo Villalobos 《Ocean & Coastal Management》2001,44(11-12)

The Mexican coast can be regionalized according to the main economic activities performed in it; for the purpose of this work we are considering five regions: North Pacific, Mar de Cortes, outh Pacific, Gulf of Mexico, and Caribbean. According to the national census, the population of the coastal zone in Mexico is increasing at a higher rate than the national average. The main industries located in the coastal and marine zones are oil and gas, fisheries, aquaculture, tourism, maritime transportation and ports, chemical industries, and minerals. Mexico has developed an environmental legal framework based on the Ley General del Equilibrio Ecologico y la Proteccion al Ambiente (LGEEPA), and the coastal management paradigm is strengthened through several other legal tools developed specifically for this purpose. There are three management strategies identified in this work for the coastal zone in Mexico: (1) Agency Leadership, (2) Protected Areas, and (3) Land Ordinance. Each one of these strategies includes stages for eventually developing an Integrated Coastal Zone Management (ICZM) plan that considers vertical and horizontal integration, scientific research of natural resources and ecosystems, and socioeconomic issues.  相似文献   

Sediment distribution patterns on the Galicia-Minho continental shelf   总被引：1，自引：0，他引：1  

J. M. A. Dias  R. Gonzalez  C. Garcia  V. Diaz-del-Rio 《Progress in Oceanography》2002,52(2-4)

A sedimentological and bathymetric study of the Minho-Galicia Shelf shows a strong contrast between a southern shelf region with a thin partially relict cover of sands and gravel, and a northern region where fine-grained sediments predominate. This contrast is explained through differences in the sediment supply, the oceanographic environment (storms and ocean currents) and the morphology of the shelf which results from its underlying tectonic framework.Most sediment is supplied to the Galicia-Minho Shelf by river discharges onto the Minho Shelf, particularly that from the Douro River. In the northern part of the shelf the Galician Rías act as sediment traps rather than sediment suppliers. The bulk of the sediment washes out of the rivers during episodic storm events. While most of the coarse sediments remain deposited close to the coast, the fine-grained material is exported to the outer areas of the shelf. Subsequently, coarse sediments close to the coast are transported southwards by the littoral drift. Whereas the fine-grained material is frequently resuspended through the action of the large swells who influence reaches deep into the water. This frequent resuspension has a long-term sorting effect on the sediments. Furthermore, resuspended sediments on the middle and outer regions of the shelf are transported northwards by a poleward flowing bottom current.As a consequence of the differential transport of coarse sediments to the south, and of the fine-grained sediments to the north, the outer reaches of the Minho Shelf are relatively poor in recent sediments. In many areas relict sediments as well as features associated with ancient coastlines and river mouths, still appear as seabed features. In contrast, the northern regions of the shelf are covered by a thin veneer of fine-grained material that smooth other most of these fossil features.The fine-grained sediment fractions (mostly very fine sands to coarse silts) are deposited in two large mud patches, the Douro and the Galicia Mud Patches, which are situated at water depths of around 100–120 m. These two mud patches are both controlled by the local hydrodynamics and morphology. The Beiral de Viana, to the west of the Douro Mud Patch is a plateau, up to 20 m high lying parallel to the shelf-break and is a morphological expression of an underlying horst system. This plateau acts as a barrier that prevents the drift of some of the fine-grained material to the west, out over the shelf-break and the continental slope. The Galicia Mud Patch is situated on the eastern part of the Galician Shelf to the north of the Douro Mud Patch. It is situated near the extension of the Porto–Tomar fault, which results in the shelf being usually steep in this region, down to a depth of about 100 m. West of this area the slope is much more gentle. Northward transport of the sediment is strongly reduced by the E–W trending outcrops of plutonic and metamorphic rocks.  相似文献   

Age and growth of the short-finned squid Illex coindetii in Galician waters (NW Spain) based on statolith analysis   总被引：1，自引：0，他引：1  

Gonzalez  Angel F.; Castro  Bernardino G.; Guerra  Angel 《ICES Journal of Marine Science》1996,53(5):802-810

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Relationships between sea surface temperature, salinity, and pelagic fish distribution off northern Chile   总被引：2，自引：0，他引：2  

Castillo  J.; Barbieri  M. A.; Gonzalez  A. 《ICES Journal of Marine Science》1996,53(2):139-146

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Surveillance and enforcement operations in the Costa Rican tuna fishery     

Luis Guillermo Lepiz  Jon G. Sutinen 《Marine Policy》1985,9(4):310-321

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Commercial whaling,tourism, and boycotts: An economic perspective     

Guillermo E. Herrera  Porter Hoagland 《Marine Policy》2006

Commercial whaling is highly contentious, angering animal rights groups and conservation organizations, who threaten boycotts. Proponents of whaling argue that many whale stocks are plentiful enough to support sustainable harvests. In terms of economic efficiency, a nation's decision to engage in whaling depends on rents from the whaling industry, ecological and market linkages, and the potential for boycotts. We analyze the tradeoffs involved in a nation's decision to engage in whaling, whale-watching, and fishing. Scenarios exist in which whaling is economically rational. Indeed, sometimes it makes economic sense to subsidize whaling. In other circumstances, market pressures make commercial whaling inefficient.  相似文献   

Volcanic particles in agriculture and gardening          下载免费PDF全文

Valentin R. Troll  Juan Carlos Carracedo  Beatrice Jägerup  Michael Streng  Abigail K. Barker  Frances M. Deegan  Francisco Perez‐Torrado  Alejandro Rodriguez‐Gonzalez  Harri Geiger 《Geology Today》2017,33(4):148-154

Volcanic pyroclasts of small size, such as lapilli and small pumice stones, are widely used in agriculture, gardening, and for pot plants as natural inorganic mulch. The technique of using pyroclasts to enhance topsoil stems from the eighteenth century, and specifically from the ad 1730–1736 eruption on Lanzarote. Critical observations on plant development during and after the eruption showed that the vegetation died when buried under a thick layer of lapilli, but grew vigorously when covered thinly. While the agriculture of Lanzarote was restricted to cereals before the eruption, it diversified to many kinds of fruit and vegetables afterwards, including the production of the famous Malvasía wines in the Canaries. The population of Lanzarote doubled in the years after the eruption, from about 5000 in 1730 to near 10 000 in 1768, predominantly as a result of the higher agricultural productivity. This outcome led to widespread use of lapilli and pumice fragments throughout the islands and eventually the rest of the globe. Lapilli and pumice provide vesicle space for moisture to be retained longer within the planting soil, which can create an environment for micro‐bacteria to thrive in. Through this route, nutrients from volcanic matter are transported into the surrounding soil where they become available to plant life. The detailed processes that operate within the pyroclasts are less well understood, such as the breakdown of nutrients from the rock matrix and transport into the soil by biological action. Further studies promise significant potential to optimize future agricultural efforts, particularly in otherwise arid areas of the globe.  相似文献