Qualitative interpretation of magnetotelluric data using the determinent apparent resistivity: Case history from the San Cayetano thrust

1993 ◽  
Author(s):  
D. E. Eggers
Keyword(s):  
Case History ◽  
Apparent Resistivity ◽  
Magnetotelluric Data ◽  
Qualitative Interpretation

THEORETICAL HORIZONTAL RESISTIVITY PROFILES OVER HEMISPHERICAL SINKS

Geophysics ◽  
1961 ◽  
Vol 26 (3) ◽  
pp. 342-354 ◽  
Author(s):  
Kenneth L. Cook ◽  
Russel L. Gray
Keyword(s):  
Digital Computer ◽  
Apparent Resistivity ◽  
Reflection Factor ◽  
General Utility ◽  
Qualitative Interpretation ◽  
Electrode Separation

An album of 40 sets (about 200 different curves) of theoretical horizontal resistivity profiles over and near outcropping hemispherical sinks shows the effects of sink diameter, reflection factor k, and distance of the traverse from the center of the sink upon the magnitude and shape of the apparent resistivity curves. Curves for sink diameters of 16a, 8a, 6a, 4a, 2a, a, and 0.5a, and reflection factors k of ±0.8, ±0.6, ±0.4, and ±0.2 are included. The values of apparent resistivity for both the Lee and Wenner configurations were computed using a digital computer. In general, the larger the sink, the larger the magnitude of the apparent resistivity anomaly up to a sink diameter of about 8a, for which the apparent resistivity over the central part of the sink is essentially equal to the resistivity of the sink, irrespective of the reflection factor. For sink diameters equal to the electrode separation a, large apparent resistivity anomalies result from “pseudo‐focusing” effects. The major peaks of the apparent resistivity curves, which lie outside the edges of the sink for negative reflection factors and inside for positive reflection factors, can be used to detect the edges of the sinks. The album of curves provides a general utility for the qualitative interpretation of apparent resistivity anomalies over features other than hemispherical sinks, such as faults (for large sinks), dikes, grabens, and similar features.

Comparison of induced polarization and controlled‐source audio‐magnetotellurics methods for massive chalcopyrite exploration in a volcanic area

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1087-1096 ◽  
Author(s):  
A. T. Basokur ◽  
T. M. Rasmussen ◽  
C. Kaya ◽  
Y. Altun ◽  
K. Aktas
Keyword(s):  
Apparent Resistivity ◽  
Field Experiments ◽  
Induced Polarization ◽  
Test Area ◽  
Volcanic Area ◽  
Far Field ◽  
Controlled Source ◽  
Ore Body ◽  
Qualitative Interpretation ◽  
Dipole Length

In this paper, we compare and contrast the results of field experiments with the dipole‐dipole‐induced polarization (IP) and controlled‐source audio‐magnetotellurics (CSAMT) methods, along the same survey profiles, at a test area that was subject to extensive drilling and detailed geological investigation. The ore bodies are interbedded between two series of dacitic tuff. The depth and thickness of the massive chalcopyrite‐pyrite‐sphalerite body vary between 25 and 100 m and 0.5 and 16 m, respectively. Resistivity and IP phase measurements on the core samples collected from the test area provide some idea of the relative differences between the background rock units and the target. The resistivity of the chalcopyrite samples varies between 0.6 to 2 ohm-m and provides sufficient resistivity contrast with surrounding volcanic rock units for target detection. The results of dipole‐dipole IP profiling with a 50-m dipole length conducted along two profiles are presented in the form of apparent resistivity and phase pseudosections. CSAMT measurements were made at 13 frequencies from 2 Hz to 8192 Hz along three profiles. The receiver dipole length was 25 m. The CSAMT data are presented in the form of pseudosections using conventional and new definitions of apparent resistivity. The elliptical contours of low apparent resistivity generated by the transition‐field notch can be misleading with respect to the real anomaly of the ore body. These artificial anomaly patterns are suppressed by making use of an alternative apparent resistivity definition derived from the frequency‐normalized impedance. The qualitative interpretation based on the IP and CSAMT pseudosections shows that the location and the extension of the ore body are indicated better in the CSAMT apparent resistivity data computed from the alternative definition. The qualitative interpretation of the IP data is difficult because of the 3-D effect arising from the neighboring thicker parts of the ore body and pyrite particles within the basement. At the final stage, the far‐field range of the CSAMT apparent resistivity and phase data is identified by the visual inspection of the individual sounding diagrams. The models derived from the 2-D Occam inversion carried out on the far‐field data are compared with the drill‐hole information and are found to describe the actual geological situation.

Static shift of magnetotelluric data and its removal in a sedimentary basin environment

Geophysics ◽  
1988 ◽  
Vol 53 (7) ◽  
pp. 967-978 ◽  
Author(s):  
Alan G. Jones
Keyword(s):  
Electric Fields ◽  
Apparent Resistivity ◽  
Sedimentary Basin ◽  
Electrode Array ◽  
Line Length ◽  
Static Shift ◽  
Magnetotelluric Data ◽  
Near Surface ◽  
The Earth ◽  
Spatial Size

Previous modeling investigations of the static shift of magnetotelluric (MT) apparent resistivity curves have limited appeal in that the electric fields used were point measurements, whereas field observations are of voltage differences. Thus, inhomogeneities of dimension of the order of the electrode line length could not be investigated. In this paper, by using a modeling algorithm that derives point voltages rather than point electric fields, I consider the effect on the MT responses of local near‐surface distorting structures, which are both outside of, and inside, the telluric electrode array. I show that static‐shift effects are of larger spatial size but of less magnitude than would be expected from conventional modeling. Also, the field observation that static shift affects only the apparent resistivity curve but not the phase response can be replicated by the voltage difference modeling. If there exists within the earth a layer whose variation in electrical resistivity along the profile can be treated in a parametric fashion, then static shift of the apparent resistivity curves can be corrected. Deriving the modal value from a sufficient number of observations for the layer resistivity is the most useful approach.

Analysis of Anisotropic Magnetotelluric Measurements at Victoria, B.C.

1973 ◽  
Vol 10 (4) ◽  
pp. 557-570 ◽  
Author(s):  
W. Nienaber ◽  
D. R. Auld ◽  
H. W. Dosso
Keyword(s):  
Electric Field ◽  
Apparent Resistivity ◽  
Conducting Layer ◽  
Frequency Range ◽  
Entire Frequency Range ◽  
Period Range ◽  
Magnetotelluric Data ◽  
Conductivity Structure ◽  
The University ◽  
Direction Of Polarization

Magnetotelluric data were recorded at the University of Victoria for a wide period range since the summer of 1968. Data for periods between 10 s and 104 s were used for interpretation. Telluric signals were found to be strongly anisotropic for the entire frequency range. Several possible causes of this anisotropy including the land–sea interface and a geological fault at Victoria are discussed.In order to obtain a 'model' for the subsurface conductivity structure, the apparent resistivity curves for both electric field components (E parallel and E perpendicular to the direction of polarization) are combined into one interpretation. The model proposes a thin, highly conducting layer near the surface of a highly resistive earth.The validity of the rotation used in transforming anisotropic telluric data before interpretation was tested experimentally.

Misophonia: An Evidence-Based Case Report

2020 ◽  
Vol 29 (4) ◽  
pp. 685-690
Author(s):  
C. S. Vanaja ◽  
Miriam Soni Abigail
Keyword(s):  
Quality Of Life ◽  
Case Report ◽  
Case History ◽  
Pure Tone ◽  
Physiological Responses ◽  
Evidence Based ◽  
Management Option ◽  
Pure Tone Audiogram

Purpose Misophonia is a sound tolerance disorder condition in certain sounds that trigger intense emotional or physiological responses. While some persons may experience misophonia, a few patients suffer from misophonia. However, there is a dearth of literature on audiological assessment and management of persons with misophonia. The purpose of this report is to discuss the assessment of misophonia and highlight the management option that helped a patient with misophonia. Method A case study of a 26-year-old woman with the complaint of decreased tolerance to specific sounds affecting quality of life is reported. Audiological assessment differentiated misophonia from hyperacusis. Management included retraining counseling as well as desensitization and habituation therapy based on the principles described by P. J. Jastreboff and Jastreboff (2014). A misophonia questionnaire was administered at regular intervals to monitor the effectiveness of therapy. Results A detailed case history and audiological evaluations including pure-tone audiogram and Johnson Hyperacusis Index revealed the presence of misophonia. The patient benefitted from intervention, and the scores of the misophonia questionnaire indicated a decrease in the severity of the problem. Conclusions It is important to differentially diagnose misophonia and hyperacusis in persons with sound tolerance disorders. Retraining counseling as well as desensitization and habituation therapy can help patients who suffer from misophonia.

Counseling Parents at the Time of Diagnosis: Moving Toward Client-Centered Practice

2020 ◽  
pp. 1-5
Author(s):  
David Luterman
Keyword(s):  
Case History ◽  
Medical Model ◽  
Diagnostic Process ◽  
Separate Entity ◽  
Initial Examination ◽  
Personal Adjustment ◽  
Flow Of Information ◽  
Ultimate Purpose

Purpose The purpose of this article is to present a client-centered model of counseling that integrates information and personal adjustment counseling. Research has indicated that audiologists are more comfortable with counseling that is information based than with personal adjustment counseling. The prevailing model of diagnosis appears to be the medical model in which, first, a case history is taken, then testing and, finally, counseling. This model lends itself to audiologist as expert and the counseling as a separate entity based on information and advice. Further research has indicated parents retain little of the information provided in the initial examination because of their heightened emotions. This article presents a client-centered model of diagnosis in which information is provided within an emotionally safe context, enabling the parents to express their feelings and have the ability to control the flow of information. The ultimate purpose of a client-centered model is to empower parents by making them active participants in the diagnostic process rather than passive recipients. Conclusion The client-centered model has wide implications for the diagnostic process as well as for the training of students.

School-Based Speech-Language Pathologists' Adherence to Practice Guidelines for Assessment of English Learners

2020 ◽  
pp. 1-12
Author(s):  
Virginia L. Dubasik ◽  
Dubravka Svetina Valdivia
Keyword(s):  
Professional Practice ◽  
Practice Guidelines ◽  
Case History ◽  
English Learners ◽  
Online Survey ◽  
Dynamic Assessment ◽  
Federal Legislation ◽  
Assessment Practices ◽  
Speech Language Pathologists ◽  
School Based

Purpose The purpose of this study was to ascertain the extent to which school-based speech-language pathologists' (SLPs) assessment practices with individual English learners (ELs) align with federal legislation and professional practice guidelines. Specifically, we were interested in examining SLPs' use of multiple tools during individual EL assessments, as well as relationships between practices and number of types of training experiences. Method School-based SLPs in a Midwestern state were recruited in person or via e-mail to complete an online survey pertaining to assessment. Of the 562 respondents who completed the survey, 222 (39.5%) indicated past or present experience with ELs, and thus, their data were included in the analyses. The questionnaire solicited information about respondent's demographics, caseload composition, perceived knowledge and skills and training experiences pertaining to working with ELs (e.g., graduate school, self-teaching, professional conferences), and assessment practices used in schools. Results The majority of respondents reported using multiple tools rather than a single tool with each EL they assess. Case history and observation were tools used often or always by the largest number of participants. SLPs who used multiple tools reported using both direct (e.g., standardized tests, dynamic assessment) and indirect tools (e.g., case history, interviews). Analyses revealed low to moderate positive associations between tools, as well as the use of speech-language samples and number of types of training experiences. Conclusions School-based SLPs in the current study reported using EL assessment practices that comply with federal legislation and professional practice guidelines for EL assessment. These results enhance our understanding of school-based SLPs' assessment practices with ELs and may be indicative of a positive shift toward evidence-based practice.

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