Tsehaie Woldai

GPS interactive time series analysis software

Time series analysis is an important part of geodetic and geodynamic studies, especially when continuous GPS observations are used to explore areas with a low rate of deformation. In this domain, having precise and robust tools for processing and analyzing position time series is a prerequisite. To meet this requirement, a new software package called GPS Interactive Time Series Analysis was developed using the MATLAB language. Along with calculating basic statistics and quality parameters such as mean and variance, the software is capable of importing and visualizing different time series formats, determining and removing jumps and outliers, interpolating data, and producing numerical and publication quality graphical outputs. Furthermore, bivariate statistical analysis (such as correlation coefficients, curvilinear and nonlinear regression), residual analysis, and spectral analysis (such as auto-spectrum, Lomb–Scargle spectrum, evolutionary power spectrum, and wavelet power spectrum) form the main analysis features of the software.

Monitoring dewatering induced subsidence and fault reactivation using interferometric synthetic aperture radar

Using multitemporal differential interferometric synthetic aperture radar analysis integrated with pumping and site geologic data we present evidence for hydrologically induced large subsidence in and around an ongoing open‐pit mine with intensive dewatering operations. Analysis of numerous differential synthetic aperture radar interferometry (DInSAR) pairs spanning the period 1993 to 2001 reveals the abrupt appearance of these features to intervals of a few to several months. Along a section through the anomaly, we plotted dewatering associated changes in the groundwater levels at monitoring wells. We also used DInSAR to extract several individual kilometre‐lengths, centimetre amplitude normal fault reactivation events in the alluvial sediments adjacent to the mine dewatering operation. High‐resolution remote sensing analyses provide strong evidence that these features align with faults active in the last several thousand years. We interpret these reactivations as mechanically involving only the upper few hundred metres of the existing fault plane above the alluvial aquifer affected by the mine dewatering.

Local interpolation of coseismic displacements measured by InSAR

Abstract Coseismic displacements play a significant role in characterizing earthquake causative faults and understanding earthquake dynamics. They are typically measured from InSAR using pre- and post-earthquake images. The displacement map produced by InSAR may contain missing coseismic values due to the decorrelation of ASAR images. This study focused on interpolating missing values in the coseismic displacement map of the 2003 Bam earthquake using geostatistics with the aim of running a slip distribution model. The gaps were grouped into 23 patches. Variograms of the patches showed that the displacement data were spatially correlated. The variogram prepared for ordinary kriging (OK) indicated the presence of a trend and thus justified the use of universal kriging (UK). Accuracy assessment was performed in 3 ways. First, 11 patches of equal size and with an equal number of missing values generated artificially, were kriged and validated. Second, the four selected patches results were validated after shifting them to new locations without missing values and comparing them with the observed values. Finally, cross validation was performed for both types of patch at the original and shifted locations. UK results were better than OK in terms of kriging variance, mean error (ME) and root mean square error (RMSE). For both OK and UK, only 4 out of 23 patches (1, 5, 11 and 21) showed ME and RMSE values that were substantially larger than for the other patches. The accuracy assessment results were found to be satisfactory with ME and RMSE values close to zero. InSAR data inversion demonstrated the usefulness of interpolation of the missing coseismic values by improving a slip distribution model. It is therefore concluded that kriging serves as an effective tool for interpolating the missing values on a coseismic displacement map.

The RiskCity Training Package on Multi-Hazard Risk Assessment

As part of the capacity-building activities of the United Nations University-ITC School on Disaster Geo-Information Management UNU-ITC DGIM the International Institute for Geo-information Science and Earth Observation ITC has developed a training package on the application of GIS for multi-hazard risk assessment. The package, called RiskCity comprises a complete suite of exercise descriptions, together with GIS data and presentation materials on the various steps required to collect and analyze relevant spatial data for hazard, vulnerability and risk assessment in an urban environment. The package has been developed in collaboration with several partner organizations on different continents, and is used as the basis for a series of courses. Currently it is available as a distance education course.

Integrated Remote Sensing and Geophysical Investigations of the Geodynamic Activities at Lake Magadi, Southern Kenyan Rift

The tectonic lineaments and thermal structure of Lake Magadi, southern Kenyan rift system, were investigated using ASTER data and geophysical methods. Five N-S faults close to known hot springs were identified for geoelectric ground investigation. Aeromagnetic data were employed to further probe faults at greater depths and determine the Curie-point depth. Results indicate a funnel-shaped fluid-filled (mostly saline hydrothermal) zone with relatively low resistivity values of less than 1 Ω-m, separated by resistive structures to the west and east, to a depth of 75 m along the resistivity profiles. There was evidence of saline hydrothermal fluid flow toward the surface through the fault splays. The observed faults extend from the surface to a depth of 7.5 km and are probably the ones that bound the graben laterally. They serve as major conduits for the upward heat flux in the study area. The aeromagnetics spectral analysis also revealed heat source emplacement at a depth of about 12 km. The relative shallowness implies a high geothermal gradient evidenced in the surface manifestations of hot springs along the lake margins. Correlation of the heat source with the hypocenters showed that the seismogenetic zone exists directly above the magmatic intrusion, forming the commencement of geodynamic activities.

Response to comments raised on “Surface deformation caused by April 6th 2009 earthquake in L’Aquila (Italy): A comparative analysis from ENVISAT ASAR, ALOS PALSAR and ASTER” by Chini Marco; Bignami Christian and Salvatore Stramondo

Abstract This paper is a response to the comments raised by Marco et al. referring to the work of Goudarzi et al. (2011) on “Surface deformation caused by the April 6th 2009 earthquake in L’Aquila (Italy): A comparative analysis from ENVISAT ASAR, ALOS PALSAR and ASTER”. While some of the issues raised by them are relevant and appropriate, the authors believe that some of their comments arose from misunderstanding and needs some elaboration. In this paper, we address their comments and clarify the ambiguities.

The Impact of Mining on The Environment

The Tharsis-Lagunazo area, in the Province of Huelva, southwestern Spain, has a long history of mining. For over three thousand years, the contour of the land has continuously been modified and re-modified by mining activities and unplanned mine wastes to provide the present landscape. This study, making use of Lands at TM imagery from 1984 and black and white aerial photographs from 1973, was able to assess the implication and impact of mining on this area. From these datasets, it was possible to detect the number of open-pit mines, waste rock dumps, tailings, slime dams, land use/cover changes and subsurface groundwater pollution.