Here we report the discovery of cold-seep ecosystem and shallow methane hydrates (2-3 mbsf) associated with methane gas flares in the water column from the Indian EEZ for the first time. The seep-sites are located in the Krishna-Godavari (K-G) basin at water depths of 900-1800 m and are characterized by gas flares in the water-column images. The occurrence of methane gas hydrates at very shallow depths (2-3 mbsf) at some of the seep-sites is attributed to high methane flux and conducive P-T conditions, necessary for the stability of methane hydrate. Chemosymbiont bearing Bivalves (Vesicomidae, Mytilidae, Thyasiridae and Solemyidae families); Polychaetes (Siboglinidae family) and Gastropods (Provannidae family) are also identified from seep-sites.

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<p>The off Nicobar region in the Andaman Sea is witnessing frequent earthquake swarms after December 2004 Tsunamigenic earthquake in January 2005, March and October 2014, November 2015 and April 2019. In this study, we present the geophysical evidence of active volcanism in the Off Nicobar back-arc region on 21<sup>st</sup> and 22<sup>nd</sup> March 2014 based on a passive Ocean Bottom Seismometer (OBS) experiment. We detected a series of hybrid earthquake events characterized by the onset of high–frequency signal (1-10 Hz) which is followed by a long period waveform of up to 600s having a range of 0.1-1 Hz. The waveforms appear to be emergent and lack the onset of a distinct S-phase. We also observed a very high frequency (10-40 Hz) hydro-acoustic phase in the coda of long-period events.  These hybrid events are considered to be volcano-tectonic (VT) events that may trigger magmatic activities in the Off Nicobar region. We have identified and located 141 high-frequency events on 21<sup>st</sup> and 22<sup>nd</sup> March 2014 using hypocent v.3.2 program and they are distributed along NW-SE direction aligning with the submarine volcanoes defining the volcanic arc as observed in the high-resolution bathymetry data. The fault plane solution of the major high-frequency events suggests strike-slip faulting with the strike, dip and rake values of 334<sup>°</sup>, 89<sup>°</sup> and 171<sup>°</sup>, respectively along the direction of the prevalent sliver strike-slip faulting in the Andaman back-arc region. We propose that the upward movement of magma is a plausible mechanism which can explain the frequent occurrence of earthquake swarms in the off Nicobar region. The stress generated from magma movement may initially trigger shallow VT events such as faulting or dike intrusions and later generate long period ringing associated with the resonance of the magma chamber. The shallow nature of the events also generates a hydroacoustic wave which is detected in the OBS experiment as the source region is in the SOFAR channel.</p>

In a pilot investigation of dental drill noise as it affects the hearing thresholds of children and dental operators, it was found that pure-tone thresholds improved (NTS) following an operative procedure when evaluation utilized continuous-tone Békésy audiometry. In a full-scale investigation, TTS's were found under the same conditions as the pilot study when pulsed-tone stimuli were used. Continuous-tone investigation was reinstated and NTS was again elicited. The reliability of the subjects was established through test-retest at 500 Hz. Exposure time for each subject and lapsed time between the end of exposure and the onset of testing were recorded. This paper examines the procedures of the investigation and the possible explanations accounting for the discrepancy between pulsed and continuous-tone Békésy conditions. Results of the primary investigation indicated that patients did not appear to be subjected to more intense (or different) exposure relative to the operators and that “high-speed” drill-noise exposure, for the duration encountered, is relatively “safe” with regard to patient PTS. [This work was supported in part by Social and Rehabilitation Service of US, DHEW, Research and Training Center No. 7, Tufts University.]