Open Access Data Article

Gravitational Moon–Earth Forces Triggering Earthquakes in Subduction Zones

Marilia Hagen, Anibal Azevedo

Journal of Geography, Environment and Earth Science International, Page 1-14
DOI: 10.9734/JGEESI/2016/29227

In this paper, we investigated the possible interactions of the moon and Earth, mainly in the period 1996-2015. Initially, we considered the gravitational force of Moon vs. Earth by Newton’s equation.  The Moon has an elliptical orbit around the planet that reaches two points of maximum. One is the closest, the Perigee, and other the farthest is the Apogee. The Apogee and Perigee have distinct values monthly.  In our study, the Perigee force was calculated during every month, year after year.  This force creates an oscillation, which in, 13 – 14 months, completes a whole cycle. The wave period is 5400 hours as calculated. The energy generated by Moon on Earth from this closest position reaches a maximum during the Full or New Moon. We observed during these phases an enhancement of earthquakes near the shorelines of the Pacific. On the other hand, the wave minimum matches with the First or Third Quarter, but in this case, the effects of earthquakes are smaller on the same regions observed for New or Full Moon. These results indicated that external forces created by Moon- Earth system allied with internal ones are responsible for increase earthquakes in the pointed out areas. Also, the oscillating movement of Moon-Earth system provides a tool for predicting the next enhancement on earthquakes cycles.

 

Open Access Original Research Article

Application of Geospatial Technology in Watershed Delineation and Extraction of Hydrologic Characteristics in Opa Catchment, Southwestern Nigeria

Maruf Orewole, Ayorinde Kappo, Ibrahim Isa, Samuel Fatile, Isiaka Lukman, Abayomi Alaga

Journal of Geography, Environment and Earth Science International, Page 1-9
DOI: 10.9734/JGEESI/2016/29267

This study explored the opportunity offered by geospatial technology to delineate the watershed draining surface water into Opa River, Southwest Nigeria and its tributaries using a selected outlet downstream of Opa reservoir and then carried out extraction of hydrologic characteristics of the watershed. The automated delineation procedure of ArcHydro extension of ArcGIS software was used. The watershed delineated has coverage of 197.21 km2 and 17 sub-watersheds. Hydrologic Engineering Centre-Geospatial Hydrologic Modelling Extension (HEC-GeoHMS) was used to extract the hydrologic characteristic of the sub-watershed such as area, basin slope, river slope, centroid elevation and longest flow length. The division of the catchment into sub-watersheds enables matching the characteristics of each unit with soil and and land use characteristics thereby making watershed management at micro scale easier.

 

Open Access Original Research Article

Subsoil Competence Evaluation of Proposed Sites for Underground Utilities Using Non-destructive Integrated Geophysical Surveys and Geotechnical Method

O. O. Falowo, O. E. Bamidele, Y. Akindureni, E. G. Imeokparia

Journal of Geography, Environment and Earth Science International, Page 1-15
DOI: 10.9734/JGEESI/2016/29491

One common cause of structural failure is inadequate soil analysis resulting in poor foundation. Therefore in order to prevent failure occurrence of a proposed communication mast and its accessories to be buried within the subsurface at a depth not less than 5 m at Isuada and Iyere towns of Ondo State, Nigeria integrated geophysical methods involving magnetic, very low frequency electromagnetic, and electrical resistivity methods were complemented with geotechnical laboratory tests adopting the British Standards methods, with the aim of evaluating the suitability of the subsoil within the chosen sites to harbour the structure. The % of fines (clay content) of the samples was generally greater than 20% with Low/Intermediate swelling potential. All the sampled soils exhibited low moisture content in their natural state (less than 10%). The geophysical results showed that the subsoil generally composed of sandy clay, clayey sand grading into laterite with thickness of 10 m and 5 m at locality 1 and 2 respectively. The results of the geotechnical analyses showed high shear strength, cohesion and compaction characteristics. Therefore considering the results of the investigation, the proposed structure can be constructed under VES 1 and 2 at locality 1 at a maximum depth of 10 m - 20 m, but fractured zone below VES 2 must be put into consideration during the design process of the proposed structure. At locality 2, construction of the structure under VES 4 could be possible provided the soil is stabilized with competent material to a depth of 15 m. Therefore geophysical investigations combine with the geotechnical results allow excellent geo-mechanical knowledge of the basement up to 10-20 m depth.

 

Open Access Original Research Article

Evaluation of Hydrologic Response to Design Precipitations and Land Use/Land Cover Change in an Ungauged Tropical Rainforest Catchment, Southwest Nigeria

M. O. Orewole, A. A. Kappo, O. O. Orimoogunje, A. T. Salami, F. O. Ukwuoma

Journal of Geography, Environment and Earth Science International, Page 1-14
DOI: 10.9734/JGEESI/2016/29937

This study evaluated Opa catchment’s hydrologic response to design precipitations and land use/land cover change. The study involved hydrologic model building, which consisted of basin characteristics’ extraction, meteorological model and control specifications. The basin characteristics were extracted using Hydrologic Engineering Centre-Geospatial Hydrologic Modelling System (HEC-GeoHMS) extension in ArcGIS 10.0. The meteorological parameters for the model were obtained by using a design rainfall after the frequency analysis of twenty one year annual maximum historical rainfall data based on Log-Pearson type III probability distribution. The 2, 5, 10, 25, 50, 100 and 200 years return periods were analyzed out of which 2, 25, 50 and 100 return periods were selected for flood discharge and volume simulation by the model. The model was calibrated and validated using known rainfall and discharge values in the catchment before it was transferred to the whole catchment. The model was evaluated using Nash-Sutcliffe efficiency (NSE) statistics and index of agreement. The study concluded that hydrologic response to design precipitation and land use/land cover is very significant (P<0.05) and that rainfall-runoff could be modelled for ungauged watersheds using available datasets coupled with GIS techniques in order to sustainably manage the watershed and mitigate flood disasters.

 

Open Access Original Research Article

Application of Geotechnical and Geophysical Methods for Engineering Site Evaluation of Emure-Ile, Southwestern, Nigeria

O. O. Falowo, E. G. Imeokparia, O. E. Bamidele, M. P. Otuaga, V. Oluwasegunfunmi

Journal of Geography, Environment and Earth Science International, Page 1-16
DOI: 10.9734/JGEESI/2016/29609

Subsoil competence evaluation was carried out in Emure Ile area of Ondo State, Southwestern Nigeria, with the aim of evaluating the competence of the subsurface geology in hosting civil engineering structures. Geotechnical investigation involved analysis of six soil samples for mechanical strength and soil classification test. The geophysical methods used were magnetic, Very Low Frequency Electromagnetic and Electrical resistivity. The geotechnical characteristics of the sampled soils showed that the subsoil is clay-sand with medium plasticity/compressibility at moderate compaction and strength characteristics. The magnetic and VLF – EM showed a correlated fairly conductive subsoil indicating a clayey material with few structural features. The VES interpretation results delineated four subsurface layers which included the topsoil, weathered Basement, partly weathered/fractured basement and the fresh basement. The layer resistivity values for the topsoil used in this study ranged from 30 – 5220 ohm-m with layer thicknesses of between 0.5 m and 6.1 m. The depth to bedrock was generally 20 m, but could be thicker at the central part of the town i.e. greater than 20 m. Corrosivity potential of the soil was generally minimal at 10 m; therefore this depth would suit the burial of metallic objects. The competency map of the area classified the area into moderate competence (40%) and low competence (20%). Most parts of the area were underlain by moderate competent subsoil (65%), while low competence (35%) was prominent around the northwestern – southwestern parts of the study area. Therefore this work has showed the importance of integrated geophysical and geotechnical techniques in engineering subsoil characterization.