滇西地区GPS时间序列中陆地水载荷形变干扰的GRACE分辨与剔除

利用“中国大陆构造环境监测网络”在云南西部地区的13个连续GPS观测站和法国空间大地测量研究组Space Geodesy Research Group）的GRACE时变重力场资料,定量分析了该区域陆地水载荷所产生的非构造形变的量值和变化特点,探讨了利用GRACE分辨和剔除GPS观测中陆地水负荷所引起的非构造形变干扰的依据和模型.结果表明：滇西地区GPS坐标变化时间序列的垂向分量中,普遍包含有明显的年周期非构造形变波动,高值可达12mm,其中约42%源于陆地水迁徙变化所引起的负荷形变;通过主成份分析方法所获取的区域GPS共模误差与GRACE陆地水载荷形变序列的相关性高达0.87,若以GRACE扣除陆地水负荷形变,则滇西地区GPS网共模误差可消除约64%,且物理机制明确.然而,由于目前的GRACE只能有效分辨大约400km范围内陆地水载荷的整体变化,所以对于各GPS站点更加局部化的陆地水负荷非构造形变干扰,尚无法进行有效分辨.     

Investigating the time dynamics of monthly rainfall time series observed in northern Lebanon by means of the detrended fluctuation analysis and the Fisher-Shannon method

We investigate the time dynamics of monthly rainfall series intermittently recorded on seven climatic stations in northern Lebanon from 1939 to 2010 using the detrending fluctuation analysis (DFA) and the Fisher-Shannon (FS) method. The DFA is employed to study the scaling properties of the series, while the FS method to analyze their order/organization structure. The obtained results indicate that most all the stations show a significant persistent behavior, suggesting that the dynamics of the rainfall series is governed by positive feedback mechanisms. Furthermore, we found that the Fisher Information Measure (the Shannon entropy power) seems to decrease (increase) with the height of the rain gauge; this indicates that the rainfall series appear less organized and less regular for higher-located stations. Such findings could be useful for a better comprehension of the climatic regimes governing northern Lebanon.     

A metal particle from a Ca,Al-rich inclusion from the meteorite Allende,and the condensation of refractory siderophile elements

A small particle (ca. 10^?6 g) was magnetically separated from a Ca,Al-rich inclusion of the Allende meteorite. By using instrumental neutron activation analysis it was found that the elements Os, W, Re, Ir, Mo, Ru and Pt were enriched by a mean factor of about 7000 relative to Cl chondrites.A polished section of the grain showed that it consisted mainly of silicates, with a rounded particle of metal and sulfide (20 μm across) attached to it.Concentrations of up to 11% Pt were determined with the microprobe in the Ni-Fe center of the particle. Furthermore, Rh was for the first time measured in an Allende inclusion. It is enriched in about the same degree as Pt, Ir and W. The Ni-Fe center was surrounded by troilite. Mo was concentrated in the sulfide, while Os and Ru were inhomogeneously distributed over the metal + sulfide phases. The particle is interpreted as direct product of metal condensation of the solar nebula. The sulfide phase formed at lower temperatures and caused redistribution of the refractory siderophile elements. Condensation calculations for a metal alloy show that Fe and Ni are expected to be already present at higher temperatures than the condensation temperatures of pure Fe. Pt and Rh, having lower condensation temperatures than pure Fe should also be completely condensed above the condensation temperature of pure Fe. Kinetic considerations show that minimum times to grow this kind of particle should be of the order of 500 years at 10^?3 atm.     

Lithophile elements in Huronian low-Ti continental tholeiites from Canada, and evolution of the Precambrian mantle

Huronian basalts from central Ontario, Canada, dated at about 2450 Ma and associated with an early rifting episode, are classified as siliceous, low-TiNb tholeiites. They display strong enrichment in large-ion lithophile (LILE) and light rare earth (LREE) elements compared to modern oceanic lavas. The tectonic setting and geochemistry resemble Mesozoic rift-related low-Ti flood basalts, including the Ferrar Group of Antarctica, and the Parana and equivalent Etendeka volcanics of south Brazil and Namibia, respectively. High LILE/LREE ratios are also similar to subduction-related island arc tholeiites, and it is suggested that enrichment of the Huronian lithospheric mantle source occurred through ancient subduction of crustal material, probably during formation and consolidation of the Archean continental crust.Melting models suggest that Huronian subcontinental mantle source compositions, derived from least contaminated, aphyric, mafic end-members, had already undergone a complex evolution, including withdrawal of Archean basalts and hydrous enrichment in incompatible components. Despite several subsequent melting episodes and a second, probably magmatic, enrichment event, however, many aspects of the Huronian source signature were preserved, and appeared in later basaltic products of this mantle mass. Keweenawan volcanics, for example, dated at about 1100 Ma, preserve low P, Zr, Ti and HREE abundances.     

Mechanism of explosive eruption revealed by geophysical observations at the Sakurajima,Suwanosejima and Semeru volcanoes

A common sequence of phenomena associated with volcanic explosions is extracted based on seismic and ground deformation observations at 3 active volcanoes in Japan and Indonesia. Macroscopic inflation-related ground deformations are detected prior to individual explosions, while deflations are observed during eruptions. Precursory inflation occurs 5 min to several hours before eruption at the Sakurajima volcano, but just 1–2 min at Suwanosejima and 3–30 min at the Semeru volcano. The sequence commences with minor contraction, which is detected by extensometers 1.5 min before eruption at Sakurajima, as a dilatant first motion of the explosion earthquakes 0.2–0.3 s before surface explosions at Suwanosejima, and as downward tilt 4–5 s prior to eruption at the Semeru volcano. The sequence is detected for explosive eruptions with > 0.1 μrad tilt change at Sakurajima, 90% at Suwanosejima and 75% at Semeru volcanoes. It is inferred that the minor contraction is caused by a volume and pressure decrease due to the release of gas from a pocket at the top of the conduit as the gas pressure exceeds the strength of the confining plug. The subsequent violent expansion may be triggered by sudden outgassing of the water-saturated magma induced by the decrease in confining pressure.     

Magma discharge variations during the 2011 eruptions of Shinmoe-dake volcano, Japan, revealed by geodetic and satellite observations

We present precise geodetic and satellite observation-based estimations of the erupted volume and discharge rate of magma during the 2011 eruptions of Kirishima-Shinmoe-dake volcano, Japan. During these events, the type and intensity of eruption drastically changed within a week, with three major sub-Plinian eruptions on January 26 and 27, and a continuous lava extrusion from January 29 to 31. In response to each eruptive event, borehole-type tiltmeters detected deflation of a magma chamber caused by migration of magma to the surface. These measurements enabled us to estimate the geodetic volume change in the magma chamber caused by each eruptive event. Erupted volumes and discharge rates were constrained during lava extrusion using synthetic aperture radar satellite imaging of lava accumulation inside the summit crater. Combining the geodetic volume change and the volume of lava extrusion enabled the determination of the erupted volume and discharge rate during each sub-Plinian event. These precise estimates provide important information about magma storage conditions in magma chambers and eruption column dynamics, and indicate that the Shinmoe-dake eruptions occurred in a critical state between explosive and effusive eruption.     

Field observations and surface characteristics of pristine block-and-ash flow deposits from the 2006 eruption of Merapi Volcano,Java, Indonesia

A series of pristine block-and-ash flow deposits from the May–June 2006 eruption of Merapi represent an exceptional record of small-volume pyroclastic flows generated by gravitational lava-dome collapses over a period of about two months. The deposits form nine overlapping lobes reaching ~ 7 km from the summit in the Gendol River valley on the volcano's southern flank, which were produced by successive flows generated during and after the major dome-collapse event on June 14. Both, single pulse (post-June 14 events) and multiple-pulse pyroclastic flows generated by sustained dome collapses on June 14 are recognised and three types of deposits, spread over an area of 4.7 km², are distinguished, totalling 13.3 × 10⁶ m³: (1) valley-confined basal avalanche deposits (11.7 × 10⁶ m³) in the Gendol River valley, (2) overbank pyroclastic-flow and associated surge deposits (1.4 × 10⁶ m³), where parts of the basal avalanche spread laterally onto interfluves and were subsequently channeled into the surrounding river valleys and (3) dilute ash-cloud surge deposits (0.2 × 10⁶ m³) along valley margins. Variations in the distribution, surface morphology and lithology of the deposits are related to the source materials involved in individual pyroclastic-flow-forming events and varying modes of transport and deposition of the different flows. Inferred flow velocities of the largest block-and-ash flows generated on June 14 vary from 43.8–13.5 m/s for the basal avalanche and from 62.6–24.2 m/s for the ash-cloud surge. The minimum temperatures range from 400 °C for the basal avalanche to 165 °C for the overlying ash cloud. Due to the potential of being re-channeled into adjacent river valleys and flowing laterally away from the main river channel, the overbank pyroclastic flows are considered the most hazardous part of the block-and-ash flow system. The conditions that lead to their development during flow transport and deposition must be taken into account when assessing future pyroclastic flow hazards at Merapi and similar volcanoes elsewhere.     

Major,minor and trace element abundances in samples from the Apollo 17 station 7 boulder: Implications for the origin of early lunar crustal rocks

Apollo 17 station 7 boulder consortia samples were analyzed for major and minor elements by a combined semimicro atomic absorption spectrophotometric and colorimetric procedure. Lithophile trace element abundances were determined by stable isotope dilution mass spectrometry. Three matrix types samples (77135, 77115, and 77075) were found to be KREEP-rich fragment-laden melts with analogues throughout the Apollo 17 landing site. Of the five clasts analyzed, at least one (77115,19, troctolite) is thought to be a cumulate; 77135, 77115, and 77075 are thought to have originated by impact fusion of material with similar composition. This original material may represent a partial melt of a parent material of the composition of an included, shocked norite breccia (77215).     

Constraints on the dynamics of subglacial basalt eruptions from geological and geochemical observations at Kverkfjöll, NE-Iceland

The Kverkfjöll area, NE Iceland is characterised by subglacial basalt pillow lavas erupted under thick ice during the last major glaciation in Iceland. The water contents of slightly vesiculated glassy rims of pillows in six localities range from 0.85±0.03 to 1.04±0.03 wt %. The water content measurements allow the ice thickness to be estimated at between 1.2 and 1.6 km, with the range reflecting the uncertainty in the CO₂ and water contents of the melt. The upper estimates agree with other observations and models that the ice thickness in the centre of Iceland was 1.5–2.0 km at the time of the last glacial maximum. Many of the pillows in the Kverkfjöll area are characterised by vesiculated cores (40–60% vesicles) surrounded by a thick outer zone of moderately vesicular basalt (15–20% vesicles). The core contains ～1 mm diameter spherical vesicles distributed uniformly. This observation suggests a sudden decompression and vesiculation of the still molten core followed by rapid cooling. The cores are attributed to a jökulhlaup in which melt water created by the eruption is suddenly released reducing the environmental pressure. Mass balance and solubility relationships for water allow a pressure decrease to be calculated from the observed change of vesicularity of between 4.4 and 4.7 MPa depressurization equivalent to a drop in the water level in the range 440–470 m. Consideration of the thickness of solid crust around the molten cores at the time of the jökulhlaup indicates an interval of 1–3 days between pillow emplacement and the jökulhlaup. Upper limits for ice melting rates of order 10^?3 m/s are indicated. This interpretation suggests that jökulhlaups can reactivate eruptions.     

GNSS观测的2021年5月22日玛多MS7.4地震同震位移及其约束反演的滑动破裂分布

2021年5月22日青海省果洛州玛多县发生M_W7.4地震,此次地震产生的地表破裂在空间上表现出明显的分段特征.本文基于不同来源的GNSS连续观测网数据获取了此次地震的精细三维同震形变场,结果显示:观测到的最大水平位移量达到280 mm,最大垂直形变量仅为25 mm,暗示此次地震的逆冲分量较小;此次地震具有较为明显的左旋走滑特征,同震形变基本对称,在NW-SE向的影响范围更广,该方向上水平同震形变大于3 mm的震中距范围超过500 km.进而,本文以余震精定位结果和GNSS观测到的三维同震形变场为约束,构建了地表破裂线为折线、倾角为85°、倾向西南的断层模型,反演了滑动破裂分布.结果显示:滑动破裂分布在震中两侧不均匀,均破裂到地表,破裂深度达到15 km左右,最大滑移量为4.73 m,计算的矩震级为M_W7.37.该结果与余震精定位结果具有很好的一致性,破裂的极值区正好位于早期余震空区,推测该余震空区未来的发震风险性较低.最后基于反演结果模拟计算了震中区域形变和应变场,结合应变值在断层地表迹线东南侧呈现挤压特征和已有的研究成果,推测此次地震增强了巴颜喀拉块体在东部地区挤压应力的积累特征,导致东部地区发震危险性增强,值得后续跟踪研究.     

Determination of paleointensity from sedimentary and igneous rocks by the method of alternating-field remagnetization

The remanent magnetization of igneous and sedimentary rocks, if not changed by heating or by alteration of magnetic minerals, keep the information about the intensity of that magnetic field in which initial magnetization took place.It has been determined that the dependence of anhysteretic remanent magnetization of such a rock on d.c. magnetic field permits us to find the paleointensity. A method of investigation of rock specimens by means of such remagnetization is suggested and applied to determining the paleointensity for a series of Permo-Triassic rocks.     

Palaeomagnetism of Mesozoic igneous rocks from the Maranha˜o Basin,Brazil, and the time of opening of the South Atlantic

From Middle-Upper Jurassic volcanics at the western margin of the Maranha?o Basin (6.4°S, 47.4°W) 15 sites (121 samples) have a mean magnetization directionD = 3.9°,I = ?17.9° withα₉₅ = 9.3°,k = 17.9 after AF cleaning (all sites have normal polarity). This yields a pole (named SAJ₂) at 85.3°N, 82.5°E (A₉₅ = 6.9°) which is near to the other known Middle Jurassic South American pole. For 21 sites (190 samples) from Lower Cretaceous basalt intrusions from the eastern part of the Maranha?o Basin (6.5°S, 42°W) the mean direction isD = 174.7°,I = +6.0° withα₉₅ = 2.8°,k = 122 (all sites have reversed polarity) yielding a pole (SAK₉) at 83.6°N, 261°E (A₉₅ = 1.9°) in agreement with other Lower Cretaceous pole positions for South America. Comparing Mesozoic pole positions for South America and Africa in the pre-drift configuration after Bullard et al. [13] one finds a significant difference (with more than 95% probability) for the Lower Cretaceous and Middle Jurassic poles and also a probable difference for the mean Triassic poles indicating a small but probably stationary separation of the two continents from the predrift position in the Mesozoic until Lower Cretaceous time which may be due to an early rifting event.     

Optimum processing of gravimetric observations affected by the drift in a one-stage net,and the analysis of the accuracy of the results

Summary By using a general model of optimum elimination of systematic effects[5], the procedure has been developed for the optimum processing of gravimetric observations affected by the drift in a one-stage net, and statistically justified characteristics of the accuracy of the points of this net have been determined.

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Source rupture model of the 2018 Mw6.7 Iburi,Hokkaido earthquake from joint inversion of strong motion and InSAR observations

The 2018 Mw6.7 Iburi earthquake shocked the eastern Iburi region to the west of the Hidaka Collision Zone in Hokkaido,which is a destructive inland earthquake.We resolved the kinematic rupture process of the event by combining strong motions(SM)and synthetic aperture radar(SAR)images in a joint inversion.The results reveal that the duration of the whole rupture is about 17s,yielding a total seismic moment of 1.4×1019 N·m(Mw=6.7).The main slip area is located at a depth of approximately 24 km with a peak slip of～0.8m above the hypocenter.The comparison with the regional velocity model shows the earthquake was initiated in the upper mantle,while the majority of slips are located in the lower crust,which is an"aseismic"domain in the typical sandwich model.The location of the major slip area is consistent with a high-conductivity volume.We proposed a mechanism of low frictional property(＜0.3)produced by high pore pressure to explain the abnormal high dip angle and centroid depth located in the ductile lower-crust.Aftershocks are distributed in areas where the Coulomb frictional stress increases due to co-seismic displacement with a mechanism conjugating to the mainshock.