סמינר מחלקתי - החוג לגיאופיזיקה ולמדעים אטמוספריים ופלנטריים

Lev V. Eppelbaum  (Tel-Aviv Uni.)

Advanced Potential Geophysical Field Analysis for Localization of Karst Terranes in Israel and Abroad

Abstract:

Karst areas occupy about 14% of the world’s land and cause serious economic losses, which are estimated at dozens of billions dollars, set aside the physical danger. Since 1990 thousands of sinkholes have occurred along the Dead Sea coastal areas both in Israel and Jordan. Potential geophysical fields: gravity and magnetic (mainly) and self-potential and thermal (secondary) are effective means for delineation and quantitative estimation of karst terranes. These potential fields having natural origin (without any field generation), are mobile and not expensive tools of subsurface examination.

For advanced magnetic anomaly interpretation in complex environments (oblique magnetization, rugged terrain relief and unknown level of the normal field) an effective interpretation system has been developed. This system (with necessary modifications) was transferred to other potential geophysical fields. In gravity prospecting, besides nonconventional anomaly interpretation, a new scheme for the calculation of terrain relief effect has been developed that increases accuracy of the Bouguer gravity computations.

At the final stage a 3D modeling of gravity and magnetic fields has been applied. Numerous transformation methods for revealing geophysical anomalies rom the karst targets occurring in complex environments were compared between themselves. However, sometimes significantly low S/N ratio does not allow to recognizing geophysical anomalies from the desired objects. Therefore, for revealing such weak geophysical anomalies against strong noise background the recent developments in wavelet method were employed.

On the basis of applying wavelet apparatus to numerous developed typical karst models a “learning” procedure was developed that enables to perform classification of the newly arrived geophysical data. The role of remote operated geophysical surveys for the timely karst recognition is underlined. Delineations of karst and quasi-karst terranes in Israel and abroad have been shown on numerous examples.