Measurements of linear strain, ultrasonic velocity, and attenuation (Q−1) were made simultaneously as functions of confining pressure on core and outcrop samples from the Moodus, Connecticut, area. Strain measurements indicate the core samples contain cracks which formed in part by stress relief during recovery (Meglis et al., 1991). The outcrop samples have a small crack porosity compared with the cores. Closure of cracks with increasing confining pressure causes an increase in velocity and a decrease in attenuation. We present a form for the pressure dependence of the crack density parameter ε (the number of cracks of unit radius per unit volume), which was used to incorporate the influence of crack closure with pressure into models of wave velocity and attenuation in cracked solids. The crack density parameter is represented as an exponentially decreasing function of confining pressure. The pressure dependence of ε was determined from the strain measurements using the non‐self‐consistent effective modulus approach of O'Connell and Budiansky (1974), from the velocity data using the solutions of Garbin and Knopoff (1973) and Hudson (1981), and from the attenuation measurements using the frictional attenuation model of Walsh (1966). All of the models fit the data reasonably well using an exponentially decaying ε described by one decay constant τ. However, some of the data are better fit by a crack density parameter with two decay constants, reflecting a rapid decrease of ε at low pressure and a slower decrease at higher pressure. There is considerable variation among the predicted decay constants for a given sample from the different data sets. Several factors contribute to this variation. For example, the two velocity models predict a different dependence of velocity on ε, which results in a different dependence of ε on pressure. For the Q−1 data, approximating dε/dP by a function with a single decay constant results in lower τ values for Q−1 than for strain or velocity. Finally, a large anisotropy in attenuation measured in the deepest core samples indicates that scattering is a significant source of wave energy loss in these samples, and therefore a frictional attenuation mechanism alone cannot account for all the observed attenuation.

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Extensive da mage to ice occ urs during ice-structure interac ti o n by microc racking, recrystalli zati o n a nd melting, Th e obj ecti ve of this wo rk was to investigate this da m a ge process unde r confin ed-stress conditi o ns beli eved to bc assoc ia ted with impact zo nes th a t occ ur durin g ice-structure inte r ac ti on, "Da m age" refers to mi c ros truc tura l mod ifi cati o n th at causes d e teriorati on o f the m ee ha nica l prope rti es, Prior exp erimental work h as shown that a sm a ll a mo unt of defo rm a ti on causes pe rm a nent da mage in ice, leading to e nh a nced creep ra tes during subsequc nt load ing, To investigate thi s soft ening, fr es hwater g ra nul a r ice was defo rmed under m od era te confineme nt (20 :'IiPa ) a t -10°C, a t two rates which brac ket duc ti le a nd brittl e beh avio r (10 2 s I a nd 10 + s I). Sa mples were deform ed to different level s of ax ial strain up to 28,8% , Thin sec tio ns we re exam i ned to assess the prog ressive cha nges in microstructure, Bo th g ra in-bound a ry a nd intra-g ra nul a r c rac king began a t strains co rrespond ing to th e peak stress (1-2% ) fo r tests at both stra in ra tes. The peak stresses we re 23.4 MPa for the tests a t 10 2 S I a nd 9.8 MPa for th e tes ts a t 10 + s I, At strains of > 1-2%, d e n se elusters of intra-g ra nul a r crac ks b ega n to develop in th e samples tes ted a t the highe r ra te, At th e lower ra te, d yna mic rec rys ta lli zati on was a ppa rently the do min a nt defo rm a ti o n m eeha nism b eyo nd the pea k stress. The a\' C rage g r a in-size decreased stro ngly during th e fi rst few per ce nt stra in a nd then m a intained a rela tivel y stabl e va lue.

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