Reply by author to discussion by L. J. Katz and W. D. Wagner

Geophysics ◽  
1976 ◽  
Vol 41 (3) ◽  
pp. 542-543
Author(s):  
H. M. Iyer
Keyword(s):  
High Velocity ◽  
Seismic Noise ◽  
Geothermal System ◽  
Imperial Valley ◽  
Geothermal Exploration ◽  
Long Valley ◽  
Exploration Tool ◽  
Ground Noise ◽  
Favorable Conditions

Nowhere in my paper have I questioned the validity of ground noise surveys as a geothermal exploration tool. My conclusions are specifically for the Mesa geothermal anomaly in Imperial Valley, California. I do believe that geothermal seismic noise exists and can be detected under favorable conditions, as was shown at Yellowstone (Iyer and Hitchcock, 1974). At Long Valley, in spite of “1000 head of cattle nibbling” at my geophones (did Drs. Katz and Wagner get the word from the cow’s mouth, perhaps) we found indications of “high‐velocity” seismic noise associated with the geothermal system in the area (Iyer and Hitchcock, 1976).

On: “Search for Geothermal Siesmic Noise in the East Mesa Area, Imperial Valley, California,” by H. M. Iyer (GEOPHYSICS, December 1975, p. 1066–1072)

Geophysics ◽  
1976 ◽  
Vol 41 (3) ◽  
pp. 542-542
Author(s):  
Lewis J. Katz
Keyword(s):  
Geophysical Methods ◽  
Geological Structure ◽  
Well Log ◽  
Noise Sources ◽  
Imperial Valley ◽  
Geothermal Exploration ◽  
Long Valley ◽  
Exploration Tool ◽  
Cultural Noise ◽  
Inversion Techniques

Dr. Iyer rightfully points out that cultural noise sources (e.g., traffic, canals) tend to mask smaller amplitude geothermally generated microtremors. These problems have been recognized by other investigators as well. However, we take exception to his conclusions questioning the validity of groundnoise surveys as a geothermal exploration tool based solely on this study or his other survey in Long Valley, California where he had 1000 head of cattle nibbling on his geophones. Areas adjacent to cultural noise generators are not meant to be surveyed by this technique, as he points out. But what of the hundreds of other areas that are culturally silent? Results from these areas have yet to be weighed. Preliminary results from suitably applicable areas appear to have favorable indications. One prospect drilled on a groundnoise anomaly has been confirmed as a major geothermal find. Crustal inversion techniques applied to groundnoise spectra have been used to interpret geological structure. Gravity and resistivity profiles, and well log information over the same areas, have verified the groundnoise interpretations. As with many other geophysical methods, groundnoise should be used as a reconnaissance tool or in conjunction with other surveys.

Shallow Crustal Structure in the DehDasht Region (SW Iran) from Ambient Seismic Noise Tomography

2021 ◽  
Author(s):  
Nastaran Shakeri ◽  
Taghi Shirzad ◽  
Shobeir Ashkpour Motlagh ◽  
Siavash Norouzi
Keyword(s):  
Crustal Structure ◽  
High Velocity ◽  
Seismic Noise ◽  
Seismic Exploration ◽  
Propagation Path ◽  
Ambient Seismic Noise ◽  
Fast Marching Method ◽  
Fast Marching ◽  
Main Challenge ◽  
Sw Iran

<p>Zagros continental collision zone (S-SW Iran) is tectonically active and extends over 1800 km contained most part of hydrocarbon reservoirs worldwide. The DehDasht region is located in the southeast of the Dezful embayment in the Zagros fold-and-thrust belt. The existence of an evaporation layer with high velocity features is the main challenge to apply classical seismic exploration in this region. However, ambient seismic noise carries valuable information about the propagation path; hence it could be a useful tool for studying crustal structure in the DehDasht region. For this purpose, we used up to 9 months of continuous data recorded by 107 stations in the area with ~16 × ~24 km<sup>2</sup>. All stations are equipped with broadband (120s) sensors recording at 100 sps. The standard ambient seismic noise processing was done as outlined by Bensen et al. (2007), and optimize empirical Green’s function (EGF) was retrieved based on the WRMS stacking method. Afterward, Rayleigh wave dispersion measurements were calculated using the FTAN approach in the period range of 0.1-5.0 s, then the inversion procedure was performed by the Fast-Marching Method with an inversion cell size of 2×2 km. Our group velocity tomographic maps show a high velocity anomaly in the Khaviz Mountain belt (west part of the study area) is generally linked to the older, consolidated bodies while two low velocity anomalies are related to the presence of fluids and or younger structures.</p>

To: “Search for Geothermal Seismic Noise in the East Mesa Area, Imperial Valley, California,” (v. 40, December 1975, p. 1066–1072).

Geophysics ◽  
1976 ◽  
Vol 41 (2) ◽  
pp. 335-335
Author(s):  
H. M. Iyer
Keyword(s):  
Seismic Noise ◽  
Imperial Valley

In the article, “Search for Geothermal Seismic Noise in the East Mesa Area, Imperial Valley, California,” by H. M. Iyer (v. 40, December 1975, p. 1066–1072), the following corrections should be made:

scholarly journals SEARCH FOR GEOTHERMAL SEISMIC NOISE IN THE EAST MESA AREA, IMPERIAL VALLEY, CALIFORNIA

Geophysics ◽  
1975 ◽  
Vol 40 (6) ◽  
pp. 1066-1072 ◽  
Author(s):  
H. M. Iyer
Keyword(s):  
Heat Flow ◽  
Seismic Noise ◽  
Critical Evaluation ◽  
Thermal Gradients ◽  
Noise Levels ◽  
Imperial Valley ◽  
Bureau Of Reclamation ◽  
Cultural Noise ◽  
Noise Experiment ◽  
The U.S

A seismic noise experiment was conducted in the East Mesa area of Imperial Valley, California, by the U.S. Geological Survey (USGS) in May 1972. There is a pronounced heat flow anomaly over the area, and between July 1972 and the present five deep test wells have been drilled over the anomaly by the U.S. Bureau of Reclamation (U.S. Bureau of Reclamation, 1974). At the time of our survey, we were aware of results from a preliminary seismic noise survey in East Mesa by Teledyne Geotech (Douze and Sorrells, 1972). A detailed noise survey was conducted by Teledyne Geotech soon after our experiment (Geothermal Staff of Teledyne Geotech, 1972). Both the Teledyne Geotech surveys show noise levels (in the 3.0 to 5.0 hz band) 12–18 db higher over the area where the thermal gradients and heat flow reach maximum values than in the surroundings. Our results, on the other hand, show that the seismic noise field in the area is dominated by cultural noise, and it is impossible to see a noise anomaly that can be related to the geothermal phenomena in East Mesa. We think that it is important to take into account this disagreement between the two results in order to make a critical evaluation of the utility of seismic noise as a geothermal prospecting tool. The purpose of this note is to put our findings on record.

Exploring geothermal resources using active and passive EM methods in the coastal areas of volcanic islands

2021 ◽  
Author(s):  
Simon Védrine ◽  
Pascal Tarits ◽  
Mathieu Darnet ◽  
François Bretaudeau ◽  
Sophie Hautot
Keyword(s):  
High Temperature ◽  
Geothermal Field ◽  
Coastal Areas ◽  
Geothermal System ◽  
Geothermal Resources ◽  
Geothermal Exploration ◽  
Near Surface ◽  
Urbanized Areas ◽  
Transient Electromagnetism ◽  
Volcanic Islands

<p>Electromagnetic geophysical exploration plays a key role in high-temperature geothermal projects to estimate the geothermal potential of a region. The objective of an EM campaign applied to high-temperature geothermal exploration is to obtain an image of the impermeable clay cap, the permeable geothermal reservoir, and the system's heat source at depth, as these three components of the overall geothermal system have distinct electrical signatures. However, deep electromagnetic imaging in the coastal areas of volcanic islands represents a major challenge due to the presence of strong cultural noise induced by urbanized areas concentrated around the coast, the proximity to the sea, strong variations of topography and bathymetry, the small size of targets and the heterogeneity of the near surface. Our objective is the multi-scale integration of airborne transient electromagnetism (ATEM), shallow marine and in land magnetotelluric (MT) and controlled source electromagnetism (CSEM) to improve the reconstruction of deep geological structures by inversion. The contribution of the CSEM method is the key to overcoming cultural electromagnetic noise and exploiting data acquired in urbanized areas. In order to study how to integrate the different EM data, we first apply our methodology to data from a geothermal exploration campaign carried out a few years ago in Martinique in the French West Indies. Then, we present results from runs with synthetic tests for a campaign planned this year in Guadeloupe, also in the French West Indie, whose objective is to increase the production capacity of an existing geothermal field.</p>

The self‐potential method in the geothermal exploration of Greece

Geophysics ◽  
1997 ◽  
Vol 62 (6) ◽  
pp. 1715-1723 ◽  
Author(s):  
George Apostolopoulos ◽  
Ioannis Louis ◽  
Evangelos Lagios
Keyword(s):  
Surrounding Medium ◽  
Geophysical Methods ◽  
Low Frequency ◽  
Potential Method ◽  
Geothermal System ◽  
Electrode Polarization ◽  
Geothermal Exploration ◽  
Contour Maps ◽  
Tectonic Features ◽  
Self Potential

Self‐potential (SP) anomalies are generated by flows of fluid, heat, and ions in the earth. SP investigations have been used to locate and delineate sources associated with such flows in three areas of geothermal interest in Greece—Lesvos Island, Loutra Hypatis (central Greece), and Nisyros Island. A combination of geophysical methods, with SP being the primary method, has been applied in these areas. The SP method is adversely influenced by various sources of noise. Field procedures have been suggested to minimize their effects by monitoring electrode polarization and telluric activity. The interpretation of SP contour maps is preferred to using profile data. A procedure was adopted for SP interpretation, and the results were satisfactory. However, this model is based on thermoelectric sources only and is not related directly to hot fluid movement. In all three survey areas, the geothermal zones delimited by the SP interpretation in combination with data acquired by other geophysical methods result in an integrated interpretation of the geothermal system. Since SP and very‐low‐frequency (VLF) anomalies can be generated by the same geological source (i.e., geothermal, highly conductive zone), the corresponding results are compared to provide a strong indication of the presence of geothermal zones. The activity of geothermal zones affects the conductivity of the surrounding medium, which also can be detected by dc resistivity and audio‐magnetotelluric (AMT) methods. In addition, geothermal zones can be related to various interfaces or tectonic features that can be detected by gravity or seismic methods.

A numerical evaluation of electromagnetic methods in geothermal exploration

Geophysics ◽  
1996 ◽  
Vol 61 (1) ◽  
pp. 121-130 ◽  
Author(s):  
Louise Pellerin ◽  
Jeffrey M. Johnston ◽  
Gerald W. Hohmann
Keyword(s):  
Electric Field ◽  
Time Domain ◽  
Numerical Models ◽  
Field Measurements ◽  
Quality Data ◽  
Geothermal System ◽  
Geothermal Exploration ◽  
Offset Time ◽  
Clay Cap ◽  
Electric Field Measurements

The size and low resistivity of the clay cap associated with a geothermal system create a target well suited for electromagnetic (EM) methods and also make electrical detection of the underlying geothermal reservoir a challenge. Using 3-D numerical models, we evaluate four EM techniques for use in geothermal exploration: magnetotellurics (MT), controlled‐source audio magnetotellurics (CSAMT), long‐offset time‐domain EM (LOTEM), and short‐offset time‐domain EM (TEM). Our results show that all of these techniques can delineate the clay cap, but none can be said to unequivocally detect the reservoir. We do find, however, that the EM anomaly from a deep, conductive reservoir overlain by a larger, more conductive clay cap is caused by the presence of the electric charge at conductivity boundaries rather than electromagnetic induction. This means that, for detection of the reservoir, methods such as MT, which rely on electric field measurements, are superior to those where only the magnetic field is measured. The anomaly produced by boundary charges at the reservoir is subtle and will be evident only if high‐quality data are collected at closely spaced measurement sites. LOTEM electric field measurements look promising and should be useful when efficient multidimensional tools are developed for LOTEM interpretation. Although CSAMT employs electric field measurements, this method is not recommended for reservoir detection because the anomaly caused by a deep reservoir is obscured by transmitter effects that cannot be isolated reliably. A combination of CSAMT and TEM measurements appears most appropriate for delineation of the clay cap.

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