THE JAnALPUR EARTHQUAKE OF MAY 22, 1997 by H.K. Gup~ R.K. Chadha, M.N. Rao, B.L. Narayana, P. Mandal, M. Ravi Kumar andN. Kumar. Jour. Geol. Soc. India, v.50, No.7, pp.85-91.
S.K. Acharyya, Director General, Geological Survey of India, comments:
The isoseismal map and geological setting of the J abalpur earthquake has been very prom ptl y presented in the note. But it has created confusion on mcmy aspects which needs to be claritied. The isoseismal map appears to have been published without careful scrutiny and assessment. There are significant differences between tlIemap published and that prep::rred by GS! painstakingly both in shape and orientalion.,Publication of such map after mutual consultation among organisations involved as has been past practice could avoid such confusion. The geological map of the area (Fig. 4 of note) and inferred active structures are also out of focus in the note and needs to be commented.
It is curious that neither any details on macroseismic studies nor the isoseismal map was mentioned or presented by the organisation (read NGRI) in the meeting organised by DST on 11 th June, 1997, specifically convened to present the work dO~le by various Earth Science Institutes of India on the Jabalpur earthquake. In the said meeting GSI did present their tindings on macroseismic, seismotectonic and MEQ studies. It described lhe isoseismal map prepared, and circulated its preliminary report (only report from any organisation to have been circulated) but did not rush for publication as there was scope for further improvement, particularly on tJle nature and orientation of the lower isoseist envelope. It is intriguing to note such difference between what has been published based on material received on 10th June, 1997 and that were presented at the inter-departmental meeting on 11 th June. It is customary to publish isoseismal map after each large/major earthquake and OS! follows tllis practise since the days of Oldham. Isoseismal map, though prepared from descriptive and subjective data sets, has its own importance and significance and such maps are vital data source for various seismo-geological applications. Considering its importance and applied aspects GS I takes special care in collection, documentation and analysis of various macro-seismic data to pu bUsh isoseismal maps of significant eartl1quakes. This involves considerable field studies, and a large number of scientists of GSI were inducted for this job from the day one of J abalpur earthquake.
For the Uttarkashi and Killari earthquakes macro-seismic investigations were conducted following MSK scales and on both the occasion it was first published after due consultations among GSI, NGRI and IMD. It is not clear why for the Jabalpur earthquake a different scale (MM) was used in the note. This also may add to confusion.
The geological map in the note (Fig. 4) neither shows the Gondwana sediments nor records the disposition of Mahakoshal rock correctly which are major units having tectonic significance in the evolution of Narmada-S on-Lineament Zone. Further, in the paper the JabaJpur earthquake has constantly been referred to as a result of activity along tbe NSL which is a 160-200 kIn wide zone. GSI study shows tJIat the earthquake can be more specifically related to activity along the South Narmada Fault which delineates mainly the nortllern map limit of the Gondwana sediments excluding the Jabalpur and equivalent sediments. This nonnal fault has acted as a reverse fault with some strike-slip component. This was continned by field studies and supported by focal mechanism and after shock studies. A NE-SW trending thrust faul t postulated by NGRI to be the active causative structure, has no mention in the published note.
Quick dissemination of scientific data are welcome, but premature publication based on incomplete data creates unnecessary confusion.
H.K. Gupta,
and others reply:Dr. S.K. Acharyya, Director General, GSI in his comments on the above paper has basically focussed on the following aspects: 1. The isoseismals are not accurate. 2. There are comments about the meeting at DST. 3. There is a comment on the geological map. 4. The paper has been published very quickly.
Our response is as follows: The isoseismal map included in the paper was published after the scientists ofNGRI worked for several days and came out wit1l a map based on detailed observations on damaged structures, ground cracks, changes in water level etc. and interviews with several people in the earthquake affected area. Isoseismal maps prepared for any earthquake could differ as tIley are very subjective and depend upon tlle interpretation of the investigators. Two important aspects of an isoseismal map are tlle highest intensity recorded and the distance to which an earthquake is felt. As far as these two issues are concerned, there may not be a dispute that the highest intensity recorded for this earthquake was VIn on MM scale and tlle earthquake was felt to a distance of about 200 kIn by most of the people. Yes, it appears from the focal mechanism obtained from CMT solution as well as'the isoseismals that the causative fault could be in NE to ENE direction. Botll the MM and tlle MSK scales are in vogue.
It may not be appropriate to discuss what happened in the DST meeting of June 11, 1997. Regarding the geological map, our efforts to buy the available published map, pertaining to SheetNo. 55 M, from S.R.O., aSI, Hyderabad, were not successful. We therefore, referred to tlle maps of J abalpur area published in the two volumes on Central India (SpL Publ.No. 28, Geol. Surv. Ind., published in 1990; and Mem. 31, Geol. Soc. Ind. published in 1995). These show considerable variation in geological boundaries of Mahakoshal and Gondwana fonnations. We do agree and regret that while transferring the infonnation Gondwana formations were missed and as a consequence there is some discrepancy in the boundaries of the Mahakoshal Formation. However, all other major formations are included in the map. The presence of Gondwana formations in the area is mentioned in tlle text on p. 88.
NGRI has been making efforts to bring the information related with damaging earthquakes in the Indian Shield region to tlle scientific community as quickly as possible. After the occurrence of the Koyna earthquake on December 11, 1967 we published a paper in Nature (Narain and Gupta, 1968). This paper was published in March 1968 i.e. witllin 3 months of the ocurrence of the earthquake. Over tile last three years we ha ve intensified our work in Koyna region. In addition to monitoring earthquakes, we have undert1ken seismic tomography and measurement of pore fluid pressures in borewells to investigate the part played by changes in pore fluid pressures inducing eartllquakcs in the vicinity of Koyna Darn. Similarly, after dle occurrence of Latur earthquake on September 30, 1993, a paper was published in Science (Gupta, 1993) within 3 months. We are deeply cqncemed with the problem of Stable Continental Region Earthquakes. Our work bas led to organizing a Chapman Conference on S table Continental Region Earthquakes to be held in January 1998 at NGRI. (Please refer to tlle announcement in this issue of me J ouma! of Geological Society of India).
OCCURRENCE OF COBALT IN KALYADI (HASSAN DIST.) AND INGALDHAL (CHITRADURGA DIST.) SULPHIDE DEPOSITS OF KARNATAKA by T.C. Devaraju and T.T. Alapieti (1997). Jour.Geol.Soc.India, v.49, pp.597N598.
Biju Mathew, Indian Institute of Technology, Powai, Bombay 400 076, comments:
I express my appreciation to. the authors for their informative report on the cobalt minerals associated with sulphide ores of Kalyadi and Ingaldhal deposits. This information may help significantly in selecting suitable process technology for extraction of cobalt from these sulphide ores. However, I seek a few clarifications.
1. I would like to draw the attention of the authors to the paper published by Naqvi et al. (1997) which has not been refered to. They have discussed the occurrence and distribution of cobalt in Ingaldhal sulphides, though they didn't give the actual amount of cobalt present in the mineral.
2. In the text, authors have described the occurrence of CON pyrite at Kalyadi with help of Fig. 1. However, in Fig. 1, the so called Co-pyrite is completely enclosed by chalcopyrite, contrary to the description given in the text stating Co-pyrite is enclosed within Co-free pyrite.
3. In the description of the data of Co-pyrite from Kalyadi, page 598, second para, the whole sentence seems to be quite ambiguous and require explanation.
4. In the Tables I and II the authors have given the mineral analysis of CON pyrite and cobaltite under two different headings as "SEM analysis" and "EPMA" and the data is listed. Can the authors please enlighten me what is "SEM analysis" and how itis possible to get weight percentage of metals using just a SEM. To my knowledge Scanning Electron Microscopy is an imaging technique and with that we can study only the surfacial features of the objects. Normally minerals analysis are done by using an EDS or WDS detector which is attached to a SEM.
T.e.
Devaraju replies:We thank Mr. Biju Mathew for the interest he has evinced in our paper and fum ish the following replies to the comments raised.
I.We don't claim that ours is the first description of Co-bearing minerals from Ingaldhal and Kalyadi which is well known. We have not quoted the paper to economise space and have highlighted only whatever quantitative mineralogical information was obtained for Co-pyrite and cobaltite based on EPMA and SEMNEDS analytical data.
2. We regret interchanging of the tenns Co-free pyrite and Chalcopyrite which has happened by oversight. Corrected statement in the text (p.597) should read as "The mineral occurs as euhedral prismatic to nearly squarish crystals (measuring 50 to 100 microns) enclosed mostly in
Chalcopyrite (Fig. 1) and at times also in Co-free pyrite".
3. The statement is simple enough and should not be difficult to understand. However, for the sake of clarity it might be added that Co in the Kalyadi sulphide ore occurs almost entirely locked up in 'Co-pyrite'; the associated pyrite, chalcopyrite and other minerals (including silicates) are either virtually devoid of Co or analyse only insignificant amount of the element.
4. When stated simply as 'SEM analyses' it is generally understood as analyses obtained employing SEM fitted with EDSIWDS detector. In our case the analyses were obtained employing SEM (JEOL) fitted with EDS aild Link AN 10,000.
GEOCHEMISTRY OF ACID VOLCANICS OF DALMAGROUP,SINGHBHUM,
EASTERN INDIA by S.P. Singh; published in Jour.GeoI.Soc.India, v.49(4), 1997, pp.437-441.
Shabber H. Alvi, Dept. of Geology, Aligarh Muslim University, Aligarh 202002, comments:
The reported felsic rocks are neither genetically nor HtllOlogically well classified. They
can
best be tenned as volcaniclastic deposits.
The Dalma metavolcanic suite does not have a confonnable relationship with the Chaibasa Fonnation. Dalma metavolcanic rocks overlap or unconfonnahly overlie the Dhalbhum Fonnation (Dunn and Dey, 1942. De et al. 1963; Sarkar and Saha, 1977 and Banerjee, 1982).
The classification of DalJna metavolcanic belt into two units is not tenable. Where would the author place the intruded peridotite and serpentinite
as
well as the reported felsic rocks? The author has not mentioned any field relationship between Dalma metavolcanic rocks, high magnesian pyroclastic rocks, and the reported felsic rocks. The genetic relationship of interbedded quartzite and associated volcaniclastics is notclear.
The mineralogy of the quartzite is also not given which can decide the mode of origin of this quartzite. Once the quartzite interbeds show effecl'\ of reworking, the reported felsic rocks can not be treatedas
pyroclastic rocks.I want to know the available Held evidences that compelled the author to suggest that 'tuffs' are eolian differentiated subaqueous distal facies of subaerial volcanism in Dalma meta-volcanic belt.
A noteworthy feature ofDalma metavolcanic belt is their complete mineralogical reconstitution. Unfortunately, most of the previous attempts which identified the MORB or ocean floor affinity of Dalma suite are based on mainly major elements.They did not consider the effects of post igneous alteration processes including metmnorphism on Ole major elements.
The widely variable Ba, Zr and particularly low Sr, Y and ZrlNb ratio neither support the volcanic Origin nor a volcanic arc tectonic setting for tlle reported felsic rocks. Moreover, the bimodal character (basalt-rhyolit(~) of Dalma volcanic belt is doubtful. Why did the author neglect Ole ultrrunatic rocks/volcaniclastics?
References
BANERJEE, P.K. (1982). Stratigraphy, pcll·ology and geochemistry of some Precambrian basic volcanic and associated rocks of Sillghbhum dist., Bihar and Mayurbhal~ and Keonjhar rusts, Orissa. Mem. GeoI. SUlV. India, v.lll, 54 p. CAS. R.A.F. and WRIGHT, lY. (1987) Volcanic Successions·Modern and Ancient, Allen and Unwin, London, 528 p.
DE, A., DASSARMA, D. and BHATrACHARJEE, J. (1963) Significant volcanic features of the Dalma lavas. CUlT. Sci.,v.32(7), pp.314-315.
DUNN, J.A. and DEY, A.K. (1942) The geology and petrology of eastern Sillghbhum and surrounding areas. Mem. Geol. Surv. India, v.69(2), pp. 281-456.
FISHER, R.V. and SCHMINCKE, II.U. (1984). Pyroclastic Rocks. Springer-Verlag, Berlin, 472 p.
SARKAR, S.N. and SABA, A.K. (1977). The present status of the Precambrian stratigraphy, tectonics and geochronology of Singhbhum-Maryurbhanj-Keonjhar region, Ea~tern India. Indian. Jour. Earth Sci, S. Ray volume, Pl>. 37-65.
S.P. Singh replies:
I thank Dr Alvi for his keen interest in my paper. I would like to remind Dr Alvi that the aim of this short communication was to discuss petrogmphy and geochemistry of the felsic volcanics exposed to the north of the Dalma mnge ratllcr than presenting a detailed account of the geology of Olis belt.
The sweeping remarks of Dr Alvi regarding classification of rocks and improper use of terminology is very funny. Dr Alvi did not bother to tum tile pages of the book he has referred. He is advised to read carefully Chapter 5 of Fisher and Schmincke (1984) to understand the meaning of the terms used in my paper.
Volcanoclastic, as defined by Fisher (1961), is a wide term which includes pyroclastic, epiclastic, autoclastic, alloclastic and also those produced by subjecting any volcanic rock to tectonic processes.
Pyroclasts are instant fragments expelled directly through volcanic vents. Agglomerate is a type of pyroclastic deposit consisting essentially of juvenile bombs. Pyroclastic conglomerate is a tenn used for mixed pyroclastic-epiclastic rock which contain 25-75% pyroclasts.
Earlier workers recognised an unconformity between the Dalma Group and the underlying Dhalbbum Formation. In later classification, however, the Dhalbhum Formation forms part of the lower unit of the Dalma Group (Gupta et a1. 1980). The contact between the Chaibasa Group and the Dhalbhum Formation is conformable. Sarkar and Saba (1977) also supported this view. The field relationship between the volcanics of the Dalma range and fue reported felsic rocks is discussed in para 2, p. 438 of the paper under discussion. The mafic pyroclasts of the Dalma range grade to felsic tuffs towards north and west. In west, the tuffs are underlain by and enclose acid agglomerate/spatter and accretionary bombs up to 70x60 cm size.
The quartzite interbeds preserve fining-up cycles, generally show gradational lower and sharp upper contacts with the associated pyroclastic rocks and consist dominantly of subangular to well-rounded and elliptical to spherical grains of quartz with subordinate amount of plagioclase, felsic volcanic rock fragments, biotite, opaques and tourmaline set in a matrix of quartz, feldspars, chlorite, opaques and epidote. Quartz grains are mono- as well as polycrystalline, some are cmbayed, and large percentage of monocrystaIline quartz grains are charged with inclusions of tiny dots and acicular green mineral. This epiclastic rock received materials from underlying pyroclast and also from extrabasinal source which suffered reworking in marginal marine depOSitional setting. This type of weathering and erosion and also recycling of pyroclasts during the period of quiescence is a common phenomenon in a volcanic terrain.
Bedding, lamination, crOSS-bedding, ripple marks, wavy, lenticular and flaser beddings, ball and pillow structure, load casts, convolute bedding, and penecontemporaneous folds and faults are the importc'Ult sedimentary structures recorded in tuffs and associated epiclastic rocks in tlle northern part. Their counterpart in the west, however, lack water-borne features. Graded bedding with distinct layer of coarse quartz and feldspar crystals at the base is the most common structure here.
Volcanic origin of these rocks is indicated by the presence of mcgaspherulites, feldspar euhedra, broken and ernbayed crystals of quartz, devitritled glass, now features, occasional vesicles and lapillis. Niggli c-mg diagram and high Baand Zr concentrations are supportive evidences. Mean Ba concentration in rhyolite, chert, and graywacke is 1127,400, and 316 ppm respectively. Low
P20S is also typical of rhyolite. Rb concentration with respect to Y +Nb values, low concentration of TI02, Nb and Y, and high ZrlNb have been used as indicator of volcanic arc tectonic setting.
References
FISHER, R.V. (1961) Proposed classification of volcaniclastic sediments and rocks. GeoI.Soc.Am.Bull.,v.72, pp.1409-1414
GUPTA, A., BASU, A. and GHOSH. P.K. (1980) The Proterozoic ultramafic and mafic lavas and tuffs of the Dalma greenstone belt, Singhbhulll, eastern Ind~a; Canadian Jour. Earth ScL, v.17(2), pp.210-231.
SARKAR, S.N. and SAHA, A.K. (1977) TIle present status of the Precambrian stratigraphy, tectonics and geochronology of Sin£hbhulll-Mayurbhanj-Keonjhar region, Eastern India. Indian Jour. Earth Sci., S. Ray volume, pp.37-65.
