Non-linear model error and resolution properties from two-dimensional single and joint inversions of direct current resistivity and radiomagnetotelluric data

For the first time, a comparative analysis of the resolution and variance properties of 2-D models of electrical resistivity derived from single and joint inversions of dc resistivity (DCR) and radiomagnetotelluric (RMT) measurements is presented. DCR and RMT data are inverted with a smoothness-constrained 2-D scheme. Model resolution, model variance and data resolution analyses are performed both with a classical linearized scheme that employs the smoothness-constrained generalized inverse and a non-linear truncated singular value decomposition (TSVD). In the latter method, the model regularization used in the inversion is avoided and non-linear semi-axes give an approximate description of the non-linear confidence surface in the directions of the model eigenvectors. Hence, this method analyses the constraints that can be provided by the data. Model error estimates are checked against improved and independent estimates of model variability from most-squares inversions. For single and joint inverse models of synthetic data sets, the smoothness-constrained scheme suggests relatively small model errors (typically up to 30 to 40 per cent) and resolving kernels that are spread over several cells in the vicinity of the investigated cell. Linearized smoothness-constrained errors are in good agreement with the corresponding most-squares errors. The variability of the RMT model as estimated from non-linear semi-axes is confirmed by TSVD-based most-squares inversions for most model cells within the depth range of investigation. In contrast to this, most-squares errors of the DCR model are consistently larger than errors estimated from non-linear semi-axes except for the smallest truncation levels. The model analyses confirm previous studies that DCR data can constrain resistive and conductive structures equally well while RMT data provide superior constraints for conductive structures. The joint inversion can improve error and resolution of structures which are within the depth ranges of exploration of both methods. In such parts of the model which are outside the depth range of exploration for one method, error and resolution of the joint inverse model are close to those of the best single inversion result subject to an appropriate weighting of the different data set

The Sources of the Authority of Academic Leaders in Jordanian Universities from the Viewpoint of the Faculty Members Working with them مصادر سلطة القادة الأكاديميين في الجامعات الأردنية من وجهة نظر أعضاء هيئة التدريس العاملين فيها

Abstract: The study aimed to identify the sources of the authority of academic leaders in Jordanian universities from the viewpoint of the faculty members working with them. A random stratified sample was chosen, consisting of (384) faculty members. The survey descriptive methodology was used, and a questionnaire consisting of (27) items, distributed in (6) fields, was used. Its validity and reliability were confirmed. The study reached the following results: the degree of appreciation of the exercise of the sources of the authority of academic leaders in Jordanian universities from the viewpoint of faculty members working with them was medium. The results also indicated that there were no statistically significant differences between the means of the responses of the study sample individuals due to the type of university and college variable. there are statistically significant differences attributable to a gender variable on the field of (gravitational power, experience authority, and reward authority) and total seore; while the results indicated a statistically significant difference attributed to gender variable in the fields of (coercive authority and persuasive authority), the differences came in favor of males. the absence of statistically significant differences attributed to the variable of the academic rank in the field of (gravitational authority, the authority of experience, and the authority of persuasion); while the results indicated the presence of statistically significant differences attributed to the variable of the academic rank in the field of (coercive authority, legal authority, and reward authority) and the total. ملخص: هدفت الدراسة التعرف إلى مصادر سلطة القادة الأكاديميين في الجامعات الأردنية من وجهة نظر أعضاء هيئة التدريس العاملين فيها. وتم اختيار عينة طبقية عشوائية, بلغت (384) عضو هيئة تدريس. واستخدم المنهج الوصفي المسحي, واستخدمت استبانة, تم التأكد من صدقها وثباتها. وتوصلت الدراسة إلى النتائج الآتية: أن درجة تقدير ممارسة مصادر سلطة القادة الأكاديميين في الجامعات الأردنية من وجهة نظر أعضاء هيئة التدريس العاملين فيها جاءت متوسطة. كما دلت النتائج على عدم وجود فروق ذات دلالة احصائية تعزى لمتغير نوع الجامعة, والكلية. ووجود فروق ذات دلالة احصائية تعزى لمتغير الجنس على مجال (سلطة الجاذبية, وسلطة الخبرة, وسلطة المكافأة) والكلي؛ بينما دلت النتائج على وجود فروق ذات دلالة احصائية تعزى لمتغير الجنس على مجالي (السلطة القسرية وسلطة الاقناع), وجاءت الفروق لصالح الذكور. وعدم وجود فروق ذات دلالة احصائية تعزى لمتغير الرتبة الأكاديمية وذلك على مجال (سلطة الجاذبية, وسلطة الخبرة, وسلطة الاقناع)؛ بينما دلت النتائج على وجود فروق ذات دلالة احصائية تعزى لمتغير الرتبة الأكاديمية على مجالات (السلطة القسرية والسلطة الشرعية وسلطة المكافأة) والكلي

Integrated geophysical imaging of the Aluto-Langano geothermal field (Ethiopia)

The Aluto-Langano geothermal system is located in the central part of the Main Ethiopian Rift, one of the world\u2019s most tectonically active areas, where continental rifting has been occurring since several Ma and has yielded widespread volcanism and enhanced geothermal gradient. The geothermal system is associated to the Mt Aluto Volcanic Complex, located along the eastern margin of the rift and related to the Wonji Fault Belt, constituted by Quaternary NNE-SSW en-echelon faults. These structures are younger than the NE-SW border faults of the central Main Ethiopian Rift and were originated by a stress field oblique to the rift direction. This peculiar tectonism yielded local intense rock fracturing that may favour the development of geothermal reservoirs. In this paper, we present the results of an integrated geophysical survey carried out in 2015 over an area of about 200 km2 covering the Mt Aluto Volcanic Complex. The geophysical campaign included 162 coincident magnetotelluric and time domain electromagnetic soundings, and 207 gravity stations, partially located in the sedimentary plain surrounding the volcanic complex. Three-dimensional inversion of the full MT static-corrected tensor and geomagnetic tipper was performed in the 338-0.001 Hz band. Gravity data processing comprised digital enhancement of the residual Bouguer anomaly and 2D-3D inverse modelling. The geophysical results were compared to direct observations of stratigraphy, rock alteration and temperature available from the several deep wells drilled in the area. The magnetotelluric results imaged a low-resistivity layer which appears well correlated with the mixed alteration layer found in the wells and can be interpreted as a low-temperature clay cap. The clay-cap bottom depth is well corresponds to a change of thermal gradient. The clay cap is discontinuous, and in the central area of the volcanic complex is characterised by a dome-shape structure likely related to isotherm rising. The propilitic alteration layer, pinpointed as the 80-Ohm-m isosurface, shows two dome-shape highs. The first is NNE-trending, and may be interpreted as an upflow zone along a fault of the Wonji belt. Two productive wells are located along the borders of this area, as well as the alignements of fumaroles and altered grounds. The second is linked to a wide resistive area, located at shallow depth, where no clay cap was detected. It could be interpreted as a fossil high-temperature alteration zone reaching shallow depths, and it is associated to several fumaroles. Modeling of 2D/3D gravity data shows that the anomalies are due to shallow density variations likely related to lithology. The deep lateral variations due to structural lineaments inferred from well stratigraphy have no detectable signature. However, the trend analysis performed on the residual Bouguer anomaly (via horizontal and tilt derivative computations), allowed to identify five lineaments. Three of them exhibit NNE-SSW strike, corresponding to the Wonji Fault Belt Trend, whereas two have NNW-SSE strike, corresponding to the Red Sea Rift trend, which in this area is of minor evidence. The signature of shallow structures is then indicative of major regional structures. One of the lineaments marks the presence of a major fumarolic zone

Multidisciplinary exploration of the Tendaho Graben geothermal fields

The NW-SE trending Tendaho Graben is the major extensional feature of the Afar, Ethiopia. Rifting and volcanic activity within the graben occurred mostly between 1.8 and 0.6 Ma, but extended to at least 0.2 Ma. Very recent (0.22\u2013 0.03 Ma) activity is focused along the southern part of the younger and active Manda Hararo Rift, which is included in the north-western part of the graben. Extension gave rise to about 1600 m of vertical displacement (verified by drilling) of the basaltic Afar Stratoid sequence, over a crust with a mean thickness of about 23 km. The infill of graben, overlying the Stratoids, consists of volcanic and sedimentary deposits that have been drilled by six exploratory wells. Within the graben, two main geothermal fields have been explored by intensive geological, geochemical and geo- physical surveys over an area that approximately covers a square sector of 40x40 km. Both new and existing data sets have been integrated. The Dubti-Ayrobera system is located along the central axis of the graben. Available data, acquired in the last three decades, comprise more than two thousands gravity and magnetic stations, 229 magnetotelluric stations and structural-geological and geochemical observations. The Alalobeda system is located along the SW flank of the graben, at about 25 km from the Dubti-Ayrobera system and has been very recently stud- ied by means of gravimetric (300 stations), magnetotelluric and TDEM (140 stations) geological and geochemical surveys. The new residual magnetic anomaly map has been used to map the younger normal polarity basalt distribution and infer the location of the unknown main rift axis. The bedrock surface resulting by the 3D inversion of the new residual Bouguer anomaly enlightens the main normal faults hindered by sediments and the secondary structures represented by horsts and grabens. The three-dimensional resistivity models allow mapping the sedimentary infill of the graben, fracture zones in the Afar Stradoids bedrock and the dome-shape structure of the clay cap layer. The 2D and 3D gravimetric, magnetic and resistivity models have been integrated with the structural, geological and geochemical outcomings in order to get an updated conceptual model of the geothermal systems

3-D Magnetotelluric Image of Offshore Magmatism at the Walvis Ridge and Rift Basin

Highlights • We report on marine 3D Magnetotelluric study on Walvis Ridge • Derived 3D electrical resistivity model shows a large scale resistive zone, which we link to crustal extension due to local uplift. It might indicate the location where the hot-spot impinged on the crust prior to rifting • Smaller scale resistive region is attributed to magma ascent during rifting • Rift basin is identified by low resistivity region The Namibian continental margin marks the starting point of the Tristan da Cunha hotspot trail, the Walvis Ridge. This section of the volcanic southwestern African margin is therefore ideal to study the interaction of hotspot volcanism and rifting, which occurred in the late Jurassic/early Cretaceous. Offshore magnetotelluric data image electromagnetically the landfall of Walvis Ridge. Two large-scale high resistivity anomalies in the 3-D resistivity model indicate old magmatic intrusions related to hot-spot volcanism and rifting. The large-scale resistivity anomalies correlate with seismically identified lower crustal high velocity anomalies attributed to magmatic underplating along 2-D offshore seismic profiles. One of the high resistivity anomalies (above 500 Ωm) has three arms of approximately 100 km width and 300 km to 400 km length at 120 degree angles in the lower crust. One of the arms stretches underneath Walvis Ridge. The shape is suggestive of crustal extension due to local uplift. It might indicate the location where the hot-spot impinged on the crust prior to rifting. A second, smaller anomaly of 50 km width underneath the continent ocean boundary may be attributed to magma ascent during rifting. We attribute a low resistivity anomaly east of the continent ocean boundary and south of Walvis Ridge to the presence of a rift basin that formed prior to the rifting

Die Struktur der elektrischen Leitfähigkeit des Dead Sea Basin abgeleitet von der 2D-und 3D-Inversion der magnetotellurischen Daten

This thesis has two main aspects: (i) the investigation of the deep geo- electrical structures of the Dead Sea basin (DSB) and (ii) the development of 3D inversion of magnetotelluric (MT) data using massive parallel computers. In total, 150 magnetotelluric stations were deployed along a main profile that extends in E-W direction for ~ 110 km, crossing the southern part of the Dead Sea basin. Some areal coverage was obtained with another set of stations which were recorded along a shorter profile (~ 20 km), extending in N-S direction. The estimated transfer functions are of high to acceptable data quality. Dimensionality and directionality analyses of the measured data show that the MT stations can be subdivided in three distinct segments. MT data from eastern and western segments are consistent with 2D assumptions and indicate a stable geo-electric strike direction of ~N10°E. Data from the central segment appear to be more affected by underlying 3D structures. A series of 2D conductivity models were computed for the main profile, using different combinations of data components and constrained inversion tests to analyse the stability of the various conductivity structures. The preferred 2D model consists of structures which can in general be well correlated with geological, tectonic and stratigraphical information. In particular, the transition from sedimentary formations into the crystalline basement is imaged clearly to the east and west of the Dead Sea basin. The surface traces of the eastern and western boundary faults appear in the 2D conductivity models as lateral conductivity contrasts from conductive structures in the central part to resistive structures in the eastern and western segments of the profile. The Al-Lisan salt intrusion appears as a resistive feature in the DSB. A very pronounced and robust feature in the 2D models is a sub-vertical conductor beneath the DSB which extends to depths of at least 70 km. For a 3D interpretation of the MT data, a new parallel inversion scheme was developed in the framework of this thesis. Three-dimensional modelling of MT data requires enormous computational resources because of the huge number of data and model parameters. To overcome these difficulties the solution of the underlying differential equation systems was parallelized for different periods and electrical current system orientations (modes). The computationally most expensive step is the linearized inversion scheme for 3D inversion, because it makes explicit use of the sensitivity matrix J and cross products in form of JJ-transpose. The dimension of this matrix depends on the number of data points and model parameters and can exceed billions of elements. Analysing the structure of this matrix revealed that it can be decomposed into blocks containing the sensitivity values corresponding to one period and one station. Distributing the computation of the blocks among several processors reduces the computation time and also the memory needed to save the sensitivity matrix. However, it is necessary to find a best compromise between communication to exchange blocks between processors and computational performance when carrying out the cross products JJ-transpose. Three-dimensional inversion tests showed that the total run time can be reduced from 5 days using four processors to less than one day using 250 processors for a certain data and model parameters. At the same time, the memory requirements were reduced from 6 GB to less than 20 MB per processor. The MT data collected in the Dead Sea area were inverted using the developed parallel 3D inversion scheme. The obtained 3D models show similarities and differences when compared with the 2D inversion results. There is general agreement with the conductivity structures obtained for the upper crust, i.e. the sedimentary sequences at the rift shoulders and their transition to the basement. However, the N-S extension of the Dead Sea brines, which is an obvious 3D feature, and underlying sedimentary basin are reflected in the 3D model as very conductive structures. The image of the Al-Lisan salt diapir appears more realistic in the 3D model as a confined resistive structure embedded in the high conductivity signature of the Dead Sea basin.Die vorliegende Dissertation betrachtet zwei Themen: (i) die Untersuchung der tiefen geoelektrischen Strukturen des Toten-Meer-Beckens (DSB) und (ii) die Parallelisierung der 3D-Inversion magnetotellurischer (MT) Daten. Insgesamt wurden 150 Magnetotellurik-Stationen entlang eines ~ 110km langen Hauptprofils installiert, das in Ost-West-Richtung den südlichen Teil des Toten-Meer- Beckens überquert. Im Bereich des Beckens wurde eine räumliche Abdeckung durch zusätzliche Stationen erlangt, die auf einem kürzeren (~ 20 km) Nord-Süd- Profil vermessen wurden. Die berechneten Übertragungsfunktionen besitzen eine annehmbare bis sehr gute Qualität. Dimensionalitäts- und Streichrichtungsanalysen der Messdaten ermöglichen eine Unterteilung der MT- Stationen in drei Bereiche: MT-Daten von den östlichen und westlichen Hauptprofilabschnitten zeigen ein 2D-Verhalten und weisen eine stabile geoelektrische Streichrichtung von ~ N10°E auf. Im mittleren Abschnitt scheinen die Daten stärker von darunter liegenden 3D Strukturen beeinflusst zu sein. Für das Hauptprofil wurde eine Vielzahl von 2D-Leitfähigkeitsmodellen berechnet. Dabei wurden unterschiedliche Kombinationen von Datenkomponenten verwendet und Inversionstests durchgeführt, um die Stabilität der verschiedenen Leitfähigkeitsstrukturen zu untersuchen. Das bevorzugte 2D- Modell besteht aus Strukturen, die insgesamt gut mit geologischen, tektonischen und stratigraphischen Informationen korreliert werden können. Insbesondere der Übergang von sedimentären Formationen zum kristallinen Basement kann östlich und westlich des Toten-Meer-Beckens klar abgebildet werden. Im Bereich der Eastern und Western Boundary Faults treten im 2D-Modell laterale Leitfähigkeitskontraste zwischen hohen Leitfähigkeiten im zentralen Bereich und deutlich geringeren Leitfähigkeiten im östlichen bzw. westlichen Abschnitt des Profils auf. Die Al-Lisan Salzintrusion zeigt sich als schlecht leitfähige Struktur innerhalb des Toten-Meer-Beckens. Ein ausgeprägtes Merkmal der 2D-Modelle ist ein vertikaler Leiter unter dem Toten-Meer-Becken, der sich bis in Tiefen von mindestens 70 km erstreckt. Zur 3D-Interpretation magnetotellurischer Daten wurde im Rahmen dieser Arbeit ein parallelisiertes Inversionsschema entwickelt. Dreidimensionale Modellierungen von MT-Daten erfordern aufgrund der großen Anzahl von Daten- und Modellparametern beträchtliche Rechnerkapazitäten. Um diese zu reduzieren, wurde die Lösung des zugrundeliegenden Systems von Differentialgleichungen über die einzelnen Perioden sowie die Richtungen (Moden) des elektrischen Stromsystems parallelisiert. Der rechenaufwändigste Abschnitt ist das linearisierte Inversionsschema der 3D-Inversion, da es expliziten Gebrauch der Sensitivitätsmatrix J und des Kreuzprodukts der Form JJ-Transpose macht. Die Dimensionalität der Matrix hängt von der Anzahl von Datenpunkten und Modellparametern ab und kann eine Milliarde Elemente übersteigen. Eine Analyse der Matrixstruktur zeigte, dass sie in Blöcke zerlegt werden kann, die die Sensitivitätswerte jeweils einer Periode einer Station enthalten. Eine Verteilung der Berechnung der einzelnen Blöcke auf mehrere Prozessoren reduziert sowohl die Rechenzeit als auch den Speicherbedarf zur Speicherung der Sensitivitätsmatrix. Es ist jedoch erforderlich, einen guten Kompromiss zwischen dem Kommunikationsaufwand beim Austausch der einzelnen Blöcke zwischen den Prozessoren und der Geschwindigkeit bei der Berechnung des Kreuzproduktes JJ-Transpose zu finden. Dreidimensionale Inversionstests zeigten, dass die Gesamtlaufzeit von 5 Tagen bei Verwendung von 4 Prozessoren auf weniger als einen Tag bei Verwendung von 250 Prozessoren für eine bestimmte Daten und Modelparameters verringert werden kann. Gleichzeitig konnte der Speicherbedarf von 6 GB auf 20 MB pro Prozessor reduziert werden. Die MT-Daten aus dem Gebiet um das Tote Meer wurden mittels des parallelisierten 3D-Inversionsschemas invertiert. Im Vergleich mit den 2D- Inversionsergebnissen weist das erhaltene 3D-Modell sowohl gute Übereinstimmungen als auch deutliche Unterschiede auf. Eine allgemein gute Übereinstimmung zeigt sich für die Leitfähigkeitsstrukturen der oberen Kruste, d. h. die sedimentären Abfolgen an den Riftschultern und den Übergang zum Basement. Die Nord-Süd-Ausdehnung der Toten-Meer-Solen - eine offensichtliche 3D-Struktur - und das darunter liegende sedimentäre Becken erscheinen im 3D- Modell als äußerst leitfähige Strukturen. Der Al-Lisan Salzdiapir scheint im 3D-Modell durch eine räumlich begrenzte Struktur mit hohen Widerständen innerhalb der leitfähigen Signatur des Toten-Meer-Beckens realistischer abgebildet zu sein

Three-dimensional electrical resistivity image of the South-Central Chilean subduction zone

Highlights • 3-D magnetotelluric image of the South Chilean arc and forearc. • High conductivity zones beneath active volcanoes. • New model explains all EM transfer functions in the arc and backarc. • Induction vectors in the forearc hint at large-scale anisotropy in the crust. Abstract Based on isotropic 3-D inversion, we re-interpret long-period magnetotelluric data collected across the geotectonic structures of the South-Central Chilean continental margin at latitudes 38°–41°S and summarize results of long-period magnetotelluric (MT) investigations performed between 2000 and 2005. The new 3-D conductivity image of the South-Central Chilean subduction zone basically confirms former 2-D inversion models along three profiles and complete the previous results. The models show good electrical conductors in the tip of the continental crustal beneath the Pacific Ocean, the frequently observed forearc conductor at mid-crustal levels, a highly-conductive zone at similar levels slightly offset from the volcanic arc and a – not well-resolved – conductor in the Argentinian backarc. The subducted Nazca Plate generally appears as a resistive but discontinuous feature. Unlike before, we are now able to resolve upper crustal conductors (interpreted as magma reservoirs) beneath active Lonquimay, Villarrica, and Llaima volcanoes which were obscured in 2-D inversion. Data fit is rather satisfactory but not perfect; we attribute this to large-scale crustal anisotropy particularly beneath the Coastal Cordillera, which we cannot include into our solution for the time being

Non-linear model error and resolution properties from two-dimensional single and joint inversions of direct current resistivity and radiomagnetotelluric data

ISSN:0956-540XISSN:1365-246

Joint inversion of lake-floor electrical resistivity tomography and boat-towed radio-magnetotelluric data illustrated on synthetic data and an application from the Äspö Hard Rock Laboratory site, Sweden

The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise. Hence, joint inversion of RMT and ERT data sets may provide a better constrained model as compared to individual inversions. In this study, joint inversion of boat-towed RMT and lake-floor ERT data has for the first time been formulated and implemented. The implementation was tested on both synthetic and field data sets incorporating RMT transverse electrical mode and ERT data. Results from synthetic data demonstrate that the joint inversion yields models with better resolution compared with individual inversions. A case study from an area adjacent to the Ä spö Hard Rock Laboratory (HRL) in southeastern Sweden was used to demonstrate the implementation of the method. A 790-m-long profile comprising lake-floor ERT and boattowed RMT data combined with partial land data was used for this purpose. Joint inversions with and without weighting (applied to different data sets, vertical and horizontal model smoothness) as well as constrained joint inversions incorporating bathymetry data and water resistivity measurementswere performed. The resultingmodels delineate subsurface structures such as a major northeasterly directed fracture system, which is observed in the HRL facility underground and confirmed by boreholes. A previously uncertain weakness zone, likely a fracture system in the northern part of the profile, is inferred in this study. The fractures are highly saturated with saline water, which make them good targets of resistivity-based geophysical methods. Nevertheless, conductive sediments overlain by the lake water add further difficulty to resolve these deep fracture zones. Therefore, the joint inversion of RMT and ERT data particularly helps to improve the resolution of the resistivity models in areas where the profile traverses shallow water and land sections. Our modification of the joint inversion of RMT and ERT data improves the study of geological units underneath shallow water bodies where underground infrastructures are planned. Thus, it allows better planning and mitigating the risks and costs associated with conductive weakness zones