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listelement.badge.dso-typeЭлемент, A RECALIBRATION OF THE GARNET-OLIVINE GEOTHERMOMETER AND A NEW GEOBAROMETER FOR GARNET PERIDOTITES AND GARNET-OLIVINE-PLAGIOCLASE-BEARING GRANULITES(2007) Wu C.M.; Zhao G.C.The garnet‐olivine Fe‐Mg exchange geothermometer and the garnet‐olivine‐plagioclase geobarometer have been simultaneously calibrated using reversed experimental data based on the model reactions image and image between 900 and 1500 °C at 9.1–95.0 kbar and between 4.7 and 7.0 kbar at 750–1050 °C, respectively. The resulting garnet‐olivine thermometer reproduces experimental temperatures mostly within ±75 °C and the garnet‐olivine‐plagioclase barometer reproduces experimental pressures well within ±0.19 kbar. These new thermobarometers use the same garnet and olivine activity models and are thermodynamically consistent. Application of these thermobarometers to garnet peridotites from mantle xenoliths, orogenic garnet peridotites over the world and the Adirondack olivine‐bearing metagabbros yielded reasonable P–T results. The present garnet‐olivine thermometer can be used to measure medium‐high‐grade to ultrahigh‐grade, low‐pressure to ultrahigh–high‐pressure garnet peridotites and metagabbros, whereas the garnet‐olivine‐plagioclase barometer has limited application to garnet‐olivine‐plagioclase‐bearing granulites.listelement.badge.dso-typeЭлемент, PETROGENESIS OF THE GARNET PERIDOTITE AND GARNET-FREE PERIDOTITE OF THE ZHIMAFANG ULTRAMAFIC BODY IN THE SULU ULTRAHIGH-PRESSURE METAMORPHIC BELT, EASTERN CHINA(2007) Yang J.S.; Li T.F.; Zhang Zh.M.; Zhang R.Y.; Liou J.G.The CCSD‐PP1 drillhole penetrated a 110‐m‐thick sequence of the Zhimafang ultramafic body in the Sulu ultrahigh‐pressure (UHP) metamorphic belt, east China. The sequence consists of interlayered garnet‐bearing (Grt) and garnet‐free (GF) peridotite. Eleven layers of Grt‐peridotite, ranging from 1.2 to 9.5 m in thickness, have an aggregate thickness of 54.49 m, whereas eight layers of GF‐peridotite, ranging from 2.2 to 14.2 m in thickness, have a total thickness of 57.53 m. The boundaries between the two rock types are gradational. The Grt‐peridotites have slightly higher contents of Al2O3, CaO and SiO2, and lower Mg#s (0.90–0.92) than the GF‐peridotites (Mg#s 0.91–0.93). Both contain low TiO2 (<0.05 wt%) and have higher modal abundances of enstatite (average 10 vol.%) than diopside (1–5 vol.%), typical of depleted‐type upper mantle. The diopside in these rocks has high and relatively uniform Mg# members (0.93–0.95), but highly variable Al2O3 (0.2–2.3 wt%), Na2O (0.5–2.5 wt%) and Cr2O3 (0.38–2.09 wt%). Enstatite (En92−93) contains very low Al2O3 (0–0.3 wt%). Both porphyroblastic and equigranular garnet are present. The equigranular varieties are zoned, from core to rim in Cr2O3 (3.4–4.2 wt%), MgO (18.4–17.5 wt%) and Al2O3 (21.1–20.1 wt%). Titania is very low in all the garnet, mostly <0.05 wt%. Chromite or chromium (Cr)‐spinel occur both in the Grt‐ and GF‐peridotite, and are characterized by high contents of Cr2O3 (49–58 wt%) and FeO (24–43 wt%), similar to that in iron‐rich Alpine‐type peridotites. Based on the bulk‐rock MgO–FeO compositions, the Zhimafang Grt‐peridotite probably underwent 20–30% partial melting, whereas the GF‐peridotite may have undergone as much as 35–40% partial melting, suggesting that the two rock types owe their differences to different degrees of partial melting rather than to pressure differences during metamorphism.listelement.badge.dso-typeЭлемент, RAY VELOCITY AND RAY ATTENUATION IN HOMOGENEOUS ANISOTROPIC VISCOELASTIC MEDIA(2007) Vavryčuk V.Asymptotic wave quantities such as ray velocity and ray attenuation are calculated in anisotropic viscoelastic media by using a stationary slowness vector. This vector generally is complex valued and inhomogeneous, and it predicts the complex energy velocity parallel to a ray. To compute the stationary slowness vector, one must find two independent, real-valued unit vectors that specify the directions of its real and imaginary parts. The slowness-vector inhomogeneity affects asymptotic wave quantities and complicates their computation. The critical quantities are attenuation and quality factor (Q-factor); these can vary significantly with the slowness-vector inhomogeneity. If the inhomogeneity is neglected, the attenuation and the Q-factor can be distorted distinctly by errors commensurate to the strength of the velocity anisotropy - as much as tens of percent for sedimentary rocks. The distortion applies to strongly as well as to weakly attenuative media. On the contrary, the ray velocity, which defines the wavefronts and physically corresponds to the energy velocity of a high-frequency signal propagating along a ray, is almost insensitive to the slowness-vector inhomogeneity. Hence, wavefronts can be calculated in a simplified way except for media with extremely strong anisotropy and attenuation.listelement.badge.dso-typeЭлемент, TIME-AVERAGED AND TIME-DEPENDENT ENERGY-RELATED QUANTITIES OF HARMONIC WAVES IN INHOMOGENEOUS VISCOELASTIC ANISOTROPIC MEDIA(2007) Červený V.; Pšenčík I.The energy–flux vector and other energy-related quantities play an important role in vari-ous wave propagation problems. In acoustics and seismology, the main attention has been devoted to the time-averaged energy flux of time-harmonic wavefields propagating in non-dissipative, isotropic and anisotropic media. In this paper, we investigate the energy–flux vector and other energy-related quantities of wavefields propagating in inhomogeneous anisotropic viscoelastic media. These quantities satisfy energy-balance equations, which have, as we show, formally different forms for real-valued wavefields with arbitrary time dependence and for time-harmonic wavefields. In case of time-harmonic wavefields, we study both time-averaged and time-dependent constituents of the energy-related quantities. We show that the energy-balance equations for time-harmonic wavefields can be obtained in two different ways. First, using real-valued wavefields satisfying the real-valued equation of motion and stress–strain relation. Second, using complex-valued wavefields satisfying the complex-valued equation of motion and stress–strain relation. The former approach yields simple results only for particularly sim-ple viscoelastic models, such as the Kelvin–Voigt model. The latter approach is considerably more general and can be applied to viscoelastic models of unrestricted anisotropy and vis-coelasticity. Both approaches, when applied to the Kelvin–Voigt viscoelastic model, yield the same expressions for the time-averaged and time-dependent constituents of all energy-related quantities and the same energy-balance equations. This indicates that the approach based on complex-valued representation of the wavefield may be used for time harmonic waves quite universally. This study also shows importance of joint consideration of time-averaged and time-dependent constituents of the energy-related quantities in some applications.listelement.badge.dso-typeЭлемент, FOCAL MECHANISMS OF RECENT EARTHQUAKES IN THE SOUTHERN KOREAN PENINSULA(2007) Park J.-C.; Kim W.; Chung T.W.; Baag C.-E.; Ree J.-H.There has been a lack of seismic data in the Korean Peninsula mainly because it is in a seismically stable area within the Eurasian plate (or Amurian microplate) and because a network of seismic stations has been poor until recently. Consequently, first motion studies on the peninsula showed a large uncertainty or covered only local areas. Also, a tectonic province map constructed based on pre-Cenozoic tectonic events in Korea has been used for a seismic zonation. To solve these problems, we made focal mechanism solutions for 71 earthquakes (ML = 1.9 to 5.2) occurred in and around the peninsula from 1999 to 2004 and collected by a new dense seismic network established since 1995. For this, we relocated the hypocenters and obtained fault plane solutions with errors of fault parameter less than 15° from the data set of 1,270 clear P-wave polarities and from 46 SH/P amplitude ratios. The focal mechanism solutions show that subhorizontal ENE P- and subhorizontal NNW T-axes are predominant, representing the common direction of P- and T-axes within the Amurian plate. The faulting mechanisms are mostly strike-slip faulting or strike-slip-dominant-oblique-slip faulting with a reverse-slip component, although normal-slip-dominant-oblique-slip faultings occur locally probably due to a local reorientation of stress. These results incorporated with those from the kinematic studies of the Quaternary faults imply that NNE-striking faults (dextral strike-slip or oblique-slip with a reverse-slip component) are highly likely to generate earthquakes in South Korea. The spatial distribution of the maximum horizontal stress direction and faulting types does not correlate with the preexisting tectonic province map of Korea, and a new construction of seismic zonation map is required for a better seismic evaluation.