S U M M A R YStrain data recorded by two crossed laser extensometers operating in the Gran Sasso underground observatory recorded seismic free oscillations excited by the 2004 December 26 Sumatra-Andaman earthquake. The main source of instrumental noise can be mitigated by differencing data from the crossed strainmeter arms, so that the resulting differential strain data set offers an unprecedented resolution of the seismic toroidal free oscillations with periods T > 1000 s. We reconstruct the time evolution of selected free-oscillations for comparison with synthetic seismograms that include normal-mode coupling effects from Coriolis force, attenuation and ellipticity. Envelopes estimated for the Gran Sasso differential data set for free oscillations with period T < 1000 s (frequencies f > 1 mHz) are approximated adequately by a composite Centroid-Moment-Tensor (CMT) source with five subevents and an aggregate M w = 9.3 moment-magnitude. Envelopes for several toroidal free oscillations with T > 1000 s are predicted less well. The amplitude of the rarely observed mode 0 T 2 is overpredicted at Gran Sasso by roughly a factor of two, and other modes are underpredicted. The amplitude discrepancy for 0 T 2 is confirmed at selected exceptionally low-noise seismic stations. Hypothetical explanations include a slow-slip component of the seismic moment release, errors in the composite-CMT source model, unmodelled coupling effects to Earth's secular modes and feedback from the Sumatra-Andaman tsunami on Indian Ocean coastlines. Of these hypotheses, either an extended-duration strain release or tsunami feedback seem most plausible. The viability of the tsunami-feedback mechansim deserves further investigation.
Purpose: Formulas linking Linear‐Quadratic (LQ) cell survival parameters to double strand break (DSB) induction are derived from the Repair‐ Misrepair‐Fixation (RMF) model for mixed radiation fields. Measured data for several cell lines irradiated by radiations of varying quality are used to examine the impact of proximity effects on intra‐ and inter‐track binary misrepair. Methods: With the RMF, estimates of alpha and beta for any particle type are determined by a well‐defined physical parameter (mean specific energy), two biological parameters (theta and kappa) that are independent of radiation quality, and a biological parameter (sigma) that depends on radiation quality. To minimize the number of ad hoc adjustable parameters, we used the published Monte Carlo Damage Simulation (MCDS) to estimate sigma. The effects of radiation quality on alpha and beta were examined by performing a regression analysis of survival data for 55 and 250 kVp x‐rays (V79 cells), for 55 kVp, 250 kVp and gamma‐rays from 60Co (CHO cells) and human kidney T‐1 cells irradiated by x‐rays, protons, deuterons and alpha particles with an LET up to 200 keV/um. Results: In CHO, V79 and T‐1 cells irradiated by widely varying types of radiation, the probability per unit time DSB formed by the same track interact in pairwise fashion is 100 to 300 times larger than the probability per unit time DSB formed by different tracks interact in pairwise fashion. Conclusion: The RMF is a useful conceptual and mathematical framework to quantify the effects of radiation quality on intrinsic radiation sensitivity for monoenergetic charged particles and mixtures of charged particles of varying quality. Although not an especially important cell killing mechanism for low LET radiations, intra‐track binary misrepair becomes the dominant one‐track cell killing mechanism for intermediate and higher LET radiations.
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