Ionospheric and geomagnetic disturbances during the 2005 Sumatran earthquakes     

Alina Marie Hasbi  Mohammed Awad Momani  Mohd Alauddin Mohd Ali  Norbahiah Misran  Kazuo Shiokawa  Yuichi Otsuka  Kiyohumi Yumoto 《Journal of Atmospheric and Solar》2009,71(17-18):1992-2005

This paper investigates the ionospheric and geomagnetic responses during the 28 March 2005 and 14 May 2005 Sumatran earthquakes using GPS and magnetometer stations located in the near zone of the epicenters. These events occurred during low solar and geomagnetic activity. TEC oscillations with periods of 5–10 min were observed about 10–24 min after the earthquakes and have horizontal propagation velocities of 922–1259 m/s. Ionospheric disturbances were observed at GPS stations located to the northeast of the epicenters, while no significant disturbances were seen relatively east and south of the epicenters. The magnetic field measurements show rapid fluctuations of 4–5 s shortly after the earthquake, followed by a Pc5 pulsation of 4.8 min about 11 min after the event. The correlation between the ionospheric and geomagnetic responses shows a good agreement in the period and time lag of the peak disturbance arrival, i.e. about 11–13 min after the earthquake.  相似文献   

Signal reconstruction of surface waves on SASW measurement using Gaussian Derivative wavelet transform     

Sri Atmaja P. Rosyidi  Mohd Raihan Taha  Zamri Chik  Amiruddin Ismail 《Acta Geophysica》2009,57(3):616-635

Surface wave method consists of measurement and processing of the dispersive Rayleigh waves recorded from two or more vertical transducers. The dispersive phase data are inverted and the shear wave velocity versus depth is obtained. However, in case of residual soil, the reliable phase spectrum curve is difficult to be produced. Noises from nature and other human-made sources disturb the generated surface wave data. In this paper, a continuous wavelet transform based on mother wavelet of Gaussian Derivative was used to analyze seismic waves in different frequency and time. Time-frequency wavelet spectrum was employed to localize the interested seismic response spectrum of generated surface waves. It can also distinguish the fundamental mode of the surface wave from the higher modes of reflected body waves. The results presented in this paper showed that the wavelet analysis is able to determine reliable surface wave spectrum of sandy clayey residual soil.  相似文献   

Comparative assessment of water surface level using different discharge prediction models     

Mokhtar  Ernieza Suhana  Pradhan  Biswajeet  Ghazali  Abd Halim  Shafri  Helmi Zulhaidi Mohd 《Natural Hazards》2017,87(2):1125-1146

Natural Hazards - Discharge is traditionally measured at gauge stations located at discrete positions along the river course. When the volume of water discharge is higher than the river bank,...  相似文献   

Behavioral of sediment transport at lowland and mountainous rivers: a special reference to selected Malaysian rivers     

Mohd Sofiyan Sulaiman  Shanker Kumar Sinnakaudan  Nik Nuraini Azhari  Roslan Zainal Abidin 《Environmental Earth Sciences》2017,76(7):300

Mountain rivers and lowland rivers differ in many ways. Some of the many elements that distinguish both river systems apart are the rivers’ geomorphological appearances, hydraulic geometry, pollution transport, sediment transport, and its own roughness and coarseness. In this particular study, the element of sediment transport is given distinctive attention too. This study employs the deterministic approach for bed load prediction entailing the use of the parameterization concept where particle size and flow variation is taken into full consideration. Apart from that, the classical approach of Shields number is also used to determine the transport rates at the fluvial system. However, due to some limitation and range of applicability, the Shields number approach was re-modified to suit the range of applicability. Changes were made to the alleviating critical stress term and formulating exponential approach. For this research, it was important to deduce the underlying principles which are universal and common to all river systems, due to obvious and distinct differences between the mountain and lowland rivers. A special attribute was given to the Malaysian natural rivers because of the limited recorded data available. All datasets were compiled and tested with the bed load predictors to observe the commonality pattern between the lowland and mountain river systems. Most of the bed load transport equations limit the range of applicability by isolating the flow regime or bed roughness individually. Thus, it was vital for researchers to find the commonality pattern between these two river systems which needed to be statistically sound in its form. It was postulated that the particle densimetric Froude number is graphically and statistically fit for both river systems. Hence, this predictor is used as it has a high potential to be included in the sediment transport parameterization for Malaysian natural rivers.  相似文献   

The GEF/UNDP/IMO Malacca Straits Demonstration Project: Sources of Pollution   总被引：1，自引：0，他引：1  

Abdul Rani Abdullah  Norhayati Mohd. Tahir  Tong Soo Loong  Tafazzal Mohd. Hoque  Abdul Halim Sulaiman 《Marine pollution bulletin》1999,39(1-12):229-233

The Straits of Malacca is subjected to a great variety of environmental stresses due to its strategic location as a major international shipping lane and the concentration of agriculture, industry and urbanisation which predominate on the west coast of Peninsular Malaysia. This paper gives an overview of the study conducted in the Malacca Straits as part of the GEF/UNDP/IMO Regional Programme on the Prevention and Management of Marine Pollution in the East Asian Seas, in particular pertaining to the identification of land and sea-based sources of pollution in Malaysia which contributes to the pollution load in the Straits, as well as the assessment of the relative contribution of each source.  相似文献   

Group velocity dispersion analysis in northern Peninsular Malaysia     

Syed Mustafizur Rahman  Md. Omar Faruk  Md. Habibur Rahman  Mumnunul Keramat  Mohd Nawawi  Faisal Kamal Zaidi 《Arabian Journal of Geosciences》2016,9(13):623

The crustal structure beneath three seismic stations over Malaysia has been investigated with the application of the group velocity dispersion analysis of the northern Sumatra earthquake data which occurred on 06 April 2010. Eighteen crustal layer models are constructed to assess the structure. Group velocity dispersions have been computed for the recorded earthquake data using a graphical method and modified Haskell matrix method for the models. Both dispersions have been presented for the interpretation of crustal layers. Findings have shown four major crustal layers having thicknesses of 2.5–4.0, 2.0–5.5, 5.0–8.0, and 8.5–9.0 km, while in Terengganu, it has shown three layers. Density, shear, and compressional wave velocities used in models have suggested that the crustal structure of the northern part of Peninsular Malaysia is crystalline. Major crustal minerals are of quartz, plagioclase, and mica. Most layers seem to have upward directions toward Perak from Kedah and Terengganu.  相似文献   

Tracer-based estimation of temporal variation of water sources: an insight from supra- and subglacial environments     

Naveen Kumar  Tirumalesh Keesari  S. Chidambaram  Shyam Ranjan  Mohd Soheb 《水文科学杂志》2013,58(11):1717-1732

ABSTRACT

The temporal variations in electrical conductivity and the stable isotopes of water, δD and δ¹⁸O, were examined at Chhota Shigri Glacier, India, to understand water sources and flow paths to discharge. Discharge is highly influenced by supraglacially derived meltwater during peak ablation, and subglacial meltwaters are more prominent at the end of the melt season. The slope of the best fit linear regression line for δD versus δ¹⁸O, for both supraglacial and runoff water, is lower than that for precipitation (snow and rain) and surface ice, indicating strong isotopic fractionation associated with the melting processes. The slope of the local meteoric water line (LMWL) is close to that of the global meteoric water line (GMWL), reflecting that the moisture source is predominantly oceanic. The d-excess variation in rainwater confirms that the southwest monsoon is the main contributor during summer while the remainder including winter is mostly influenced by westerlies.  相似文献   

A 3-tier tsunami vulnerability assessment technique for the north-west coast of Peninsular Malaysia     

H. Ismail  A. K. Abd Wahab  M. F. Mohd Amin  M. Z. Mohd Yunus  F. Jaffar Sidek  B. Esfandier J. 《Natural Hazards》2012,63(2):549-573

The 2004 tsunami that struck the Sumatra coast gave a warning sign to Malaysia that it is no longer regarded as safe from a future tsunami attack. Since the event, the Malaysian Government has formulated its plan of action by developing an integrated tsunami vulnerability assessment technique to determine the vulnerability levels of each sector along the 520-km-long coastline of the north-west coast of Peninsular Malaysia. The scope of assessment is focused on the vulnerability of the physical characteristics of the coastal area, and the vulnerability of the built environment in the area that includes building structures and infrastructures. The assessment was conducted in three distinct stages which stretched across from a macro-scale assessment to several local-scale and finally a micro-scale assessment. On a macro-scale assessment, Tsunami Impact Classification Maps were constructed based on the results of the tsunami propagation modelling of the various tsunami source scenarios. At this stage, highly impacted areas were selected for an assessment of the local hazards in the form of local flood maps based on the inundation modelling output. Tsunami heights and flood depths obtained from these maps were then used to produce the Tsunami Physical Vulnerability Index (PVI) maps. These maps recognize sectors within the selected areas that are highly vulnerable to a maximum tsunami run-up and flood event. The final stage is the development of the Structural Vulnerability Index (SVI) maps, which may qualitatively and quantitatively capture the physical and economic resources that are in the tsunami inundation zone during the worst-case scenario event. The results of the assessment in the form of GIS-based Tsunami-prone Vulnerability Index (PVI and SVI) maps are able to differentiate between the various levels of vulnerability, based on the tsunami height and inundation, the various levels of impact severity towards existing building structures, property and land use, and also indicate the resources and human settlements within the study area. Most importantly, the maps could help planners to establish a zoning scheme for potential coastline development based on its sensitivity to tsunami. As a result, some recommendations on evacuation routes and tsunami shelters in the potentially affected areas were also proposed to the Government as a tool for relief agencies to plan for safe evacuation.  相似文献   

Effect of soil hydraulic properties model on slope stability analysis based on strength reduction method   总被引：2，自引：0，他引：2  

Muhammad Mukhlisin  Marlin Ramadhan Baidillah  Aniza Ibrahim  Mohd. Raihan Taha 《Journal of the Geological Society of India》2014,83(5):586-594

Soil hydraulic properties models which have been proposed were derived based on the empirical fitting curve such as Brooks-Corey model (BC) and Van Genuchten model (VG), or based on soil pore radius distribution such as Lognormal model (LN). Each model has different accuracy for predicting soil moisture distribution. In the analysis of rainfall-induced slope failure, the soil hydraulic properties model was needed to describe the physical phenomena of behavior characteristic of water in unsaturated soil. As moisture content has an effect on soil strength, it is vital to select the suitable soil hydraulic properties model for predicting Factor of Safety (FOS) especially in forecasting landslide hazard. In this study, a numerical model of seepage finite element analysis using BC, VG, and LN model were used and compared in order to analyze the soil moisture distribution, water movement phenomenon, and slope stability characteristic in unsaturated soil slope based on the strength reduction method (SRM). The results showed that the variations of the parameters predicting the moisture content of soil leads to differences of FOS in some cases. The parametric study showed that for the unsaturated soil condition, BC model has the greatest FOS value than the other model, while VG model has the lowest. On the other hand, the FOS of all models have the same result for the saturated condition. Other than that, it was found that the increasing of ESP value in the surface layer has significant effect in the sub-surface layer.  相似文献   

REE mineralization in the carbonatites of the sung valley ultramafic-alkaline-carbonatite complex,Meghalaya, India   总被引：1，自引：0，他引：1  

Mohd. Sadiq  A. Ranjith  Ravi Kumar Umrao 《Central European Journal of Geosciences》2014,6(4):457-475

The Early Cretaceous Sung Valley Ultramafic-Alkaline-Carbonatite (SUAC) complex intruded the Proterozoic Shillong Group of rocks and located in the East Khasi Hills and West Jaintia Hills districts of Meghalaya. The SUAC complex is a bowl-shaped depression covering an area of about 26 km² and is comprised serpentinised peridotite forming the core of the complex with pyroxenite rim. Alkaline rocks are dominantly ijolite and nepheline syenite, occur as ring-shaped bodies as well as dykes. Carbonatites are, the youngest intrusive phase in the complex, where they form oval-shaped bodies, small dykes and veins. During the course of large scale mapping in parts of the Sung Valley complex, eleven carbonatite bodies were delineated. These isolated carbonatite bodies have a general NW-SE and E-W trend and vary from 20–125 m long and 10–40 m wide. Calcite carbonatite is the dominant variety and comprises minor dolomite and apatite and accessory olivine, magnetite, pyrochlore and phlogopite. The REE-bearing minerals identified in the Sung Valley carbonatites are bastnäsite-(Ce), ancylite-(Ce), belovite-(Ce), britholite-(Ce) and pyrochlore that are associated with calcite and apatite. The presence of REE carbonates and phosphates associated with REE-Nb bearing pyrochlore enhances the economic potential of the Sung Valley carbonatites. Trace-element geochemistry also reveals an enrichment of LREEs in the carbonatites and average ΣREE value of 0.102% in 26 bed rock samples. Channel samples shows average ΣREE values of 0.103 wt%. Moreover, few samples from carbonatite bodies has indicated relatively higher values for Sn, Hf, Ta and U. Since the present study focuses surface evaluation of REE, therefore, detailed subsurface exploration will be of immense help to determine the REE and other associated mineralization of the Sung Valley carbonatite prospect.  相似文献