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1.
In continent Lg is usually one of the predominant phases recorded by short-period or broad-band seismometers. A ray-theoretical approach shows that Lg wave is the superposition of higher-mode surface waves propagating in the continental crust[1—4]. The g… 相似文献
2.
利用1989～1998年间发生在中国华北地区ML≥3.0级的地震事件,华北遥测台网以及数字化台网记录到的信噪比较高的Lg尾波时间序列,经过滤波、消除背景噪声等预处理,采用单台记录叠加频谱比法,得到传播路径上Lg尾波Q0（Q=Q0fη, Q0是1Hz的Q值,η是Q值与频率相关系数）,进而获得该地区Q0和η的空间分布. 测量结果表明,华北地区地壳Lg尾波Q0值分布存在显著的横向不均匀性,这种不均匀性与该地区地壳的速度分布基本一致,表现为与该地区地表地质特征明显的一致性,即传播路径位于太行山隆起和燕山隆起区为高Q0值分布;传播路径位于冀中坳陷和黄骅坳陷等平原区表现为低Q0值;传播路径位于隆起区和坳陷区二者之间,其Q0值也介于二者之间,说明华北地区的地壳结构没有很大的阶跃式变化而使波导遭到破坏,Lg尾波Q0值基本上反映了地壳内介质滞弹性的固有衰减. 相似文献
3.
Jadeitic rocks within high pressure metamorphic zone from northeastern Jiangxi Province and their forming and surviving conditions 总被引：1，自引：0，他引：1
Guoqing Zhou 《中国科学D辑(英文版)》1997,40(5):477-484
There is a close relation in time, space and origin between the NEJXO, NEJXDFZ and HPMZ from NEJXP which are located in and
constrained by both Yangtze Craton and Cathaysia. These HPMRs principally include (i) Jd-Q-Ab schist, (ii) Lw-Jd-Ab schist,
(iii) Jd-Ab schist, and (iv) Gl-schist. The Jd is nearly pure (Jd91-98). Jd surrounded by Ab is separated from Q and survived
due to the reaction between Jd and Q, while Lw encircled by Ab remains as a pseudomorph composed of CZo+An. The minerals associated
with Jd are Lw, Gl, Ab, Q, CZo, An, Pa, II, Ru, Sp, Ap, and Zr. According to the textures, the mineral paragenesis is classified
into four groups (i) PI-Am-Q, (ii) Jd-I,w-GI-Q, (iii) CZo-An-Ab-Q, (iv) Ab-Ana-Ser-Ur, corresponding to (i) 1.0–0.93 Ga, 250°C,
2–3 × 108 Pa; (ii) 0.93–0.79 Ga, 300–350°C, 5–12 × 108 Pa; (iii) 0.79–0.223 Ga, 350–400–120°C, 12–5–3 × 108 Pa; and (iv) < 0. 223 Ga, < 120–50°C, < 3 × 108 Pa, in time, temperature and pressure respectively. A clockwiseP-T-t path is isothermal increasing inP (up to 45 km)—isothermal decreasing inP (up to 5 km)— nearly isobar decreasing in T.
Project supported by the National Natural Science Foundation of China. 相似文献
4.
利用两台架设在北京台的海底地震仪样机记的1998年1月10日6．2M张北地震的余震，选其中信噪比较高的记录利用单台叠加频谱比法得到Lg尾波Q及频率依赖因子，结果显示，所有地震的Lg尾波Q值都比较接近，并且由两台仪器记录的同一地震得到的Q值及具有较高的一致性，从中可以得出两点结论：（1）单台叠加频谱比法是求Q值的较稳定的方法，（2）两台仪器的性能比较稳定，可靠性高。 相似文献
5.
单台Lg尾波Q_(Lg)~c的测量研究 总被引：7，自引：2，他引：5
将单台记录叠加频谱比法（简称SSR法）应用于震中距小于500km的区域地震Lg尾波为lHz下的值,n是与频率f有关的指数)的提取之中·为了检验方法的稳定性和可靠性,我们选用两组发生在不同地区的地震记录．一组是1989-10-18大同主震（ML＝5．9）的15个余震,北京遥测地震台网记录到的信噪比较高的Lg尾波序列。另一组是秦岭造山带数字流动地震观测台网记录到的1995年甘肃平凉两次地震信噪比较高的Lg尾波序列．每一组地震的震源参数基本相同,即它们到某一特定台站的路径几乎相同,得到的 可以认为是不受震源影响的地震一台站路径上的平均衰减效应·两区域 的测量结果表明：（1）尽管两个地震观测台网所用观测仪器不同,每个台站的观测条件不同,所记录的地震也不尽相同,但对Q0和,的拟合结果线性程度都比较高,说明SSR法是稳定的;（2）同一震群的不同地震到某一特定台站测得的结果基本一致,即Q0值及其平均值大都在其标准差范围之内,说明SSR法是可靠的。（3）对同一地震不同方位各台站的Lg尾波测量结果可以看出,穿过不同构造区的Q0值存在明显差... 相似文献
6.
收集了昆明台1990～2000年间大于4.0级的地震宽频记录资料，以及分布在云南境内的23个昆明数字化台网1999～2000年的资料，使用单台叠加谱比方法处理了280个Lg尾波信号. 在假定Lg尾波Q与频率f有Q =Q0fη关系的基础上，计算出各射线1Hz时的Q值及频率相关因子η. 在此基础上，运用反投影技术反演得到云南及周边地区0.5°×0.5°网格内的Q0和η的分布图像. 结果表明：云南及周边地区的Q0在150～300之间变化，滇东地区的Q0明显高于滇西地区；η的变化范围在0.3～0.8之间，绝大部分地区η的变化范围为0.5～0.6. 相似文献
7.
利用单台记录叠加频谱比法测量出的华北地区560余条单台传播路径上平均Lg尾波Q0值数据（Q0是1Hz的Q值）,采用随机褶积模型和奇异值分解法,重建该地区地壳中Q0的横向变化.结果表明,华北地区地壳中Lg尾波Q0值分布具有显著的横向不均匀性,这种不均匀性与地质构造明显相关,块隆区具有较高的Q0值,例如,燕山造山带、太行山块隆、鲁西隆起;华北平原区表现为低Q0值分布,例如冀中坳陷、黄骅坳陷、济阳坳陷,二者界限分明.结合研究区内的大地热值分布研究表明,低Q0值区大都处于高热流区,这可能是地壳内热物质的活动有关.虽然华北地区Lg尾波Q0值高、低分区明显,但是,从总体上应该属于低Q0值异常区,也就是说,该区的地壳是高地震波衰减区,这可能是该地区受太平洋板块和欧亚板块的相互作用而使地壳减薄,热物质上升造成的结果. 相似文献
8.
The zone of anomalous diurnal variations in foF2, which is characterized by an excess of nighttime foF2 values over daytime ones, has been distinguished in the Southern Hemisphere based on the Intercosmos-19 satellite data.
In English literature, this zone is usually defined as the Weddell Sea anomaly (WSA). The anomaly occupies the longitudes
of 180°–360° E in the Western Hemisphere and the latitudes of 40°–80° S, and the effect is maximal (up to ∼5 MHz) at longitudes
of 255°–315° E and latitudes of 60°–70° S (50°–55° ILAT). The anomaly is observed at all levels of solar activity. The anomaly
formation causes have been considered based on calculations and qualitative analysis. For this purpose, the longitudinal variations
in the ionospheric and thermospheric parameters in the Southern Hemisphere have been analyzed in detail for near-noon and
near-midnight conditions. The analysis shows that the daytime foF2 values are much smaller in the Western Hemisphere than in the Eastern one, and, on the contrary, the nighttime values are
much larger, as a result of which the foF2 diurnal variations are anomalous. Such a character of the longitudinal effect mainly depends on the vertical plasma drift
under the action of the neutral wind and ionization by solar radiation. Other causes have also been considered: the composition
and temperature of the atmosphere, plasma flows from the plasmasphere, electric fields, particle precipitation, and the relationship
to the equatorial anomaly and the main ionospheric trough. 相似文献
9.
Based on an analysis of a large array of meteorological data, we have shown that surface air temperatures differ significantly
in years of sunspot maxima and minima for different months and latitudes and longitudes of observation points. This difference
is the greatest at high latitudes of 60–83°; it is equal to +2.07 ± 0.28°C in February in the longitudinal range of 170 ±
190° and −1.41 ± 0.29°C in November in the longitude range of 150 ± 170°. 相似文献
10.
G. A. Mansilla 《Studia Geophysica et Geodaetica》2007,51(4):563-574
An investigation of the response of the mid-high, mid and low latitude critical frequency foF2 to the geomagnetic storm of
15 July 2000 is made. Ground-based hourly foF2 values (proportional to square root of peak electron density of F2-layer) from
four chains of ionospheric stations located in the geographic longitude ranges 10°W–35°E, 60°E–120°E, 130°E–170°E, 250°E–295°E
are used. Relative deviations of foF2 are considered. The main ionospheric effects for the considered storm are: long-duration
negative disturbances at mid-high latitudes in summer hemisphere in sectors where the storm onset occurred in the afternoon/night-time
hours; short-duration positive disturbances in the summer hemisphere at mid-high latitudes in the pre-sunset hours during
the end of main phase-first stage of the recovery; small and irregular negative disturbances in the low latitude winter hemisphere
which predominate during the main phase and first part of the recovery, and positive disturbances in both hemispheres at mid-high
and mid latitudes prior to the storm onset irrespective of the local time. In addition, the validity of some physical mechanisms
proposed to explain the F2 region behaviour during disturbed conditions is considered.
gus-mansilla@hotmail.com 相似文献
11.
The optical observations on Heiss Island (Φ′ = 75.0°) have been used to study the characteristics of auroras in the near-noon
MLT sector after abrupt increases in the solar wind dynamic pressure at negative and positive polarity of the IMF B
z
component. It has been found out that the 427.8 and 557.7 nm emission intensities considerably increased at B
z
< 0 both equatorward of the dayside red luminosity band and within this band. The value of the emission intensities at a
red luminosity maximum (I
6300/I
5577 ∼ 0.5) indicates that energetic electron precipitation is of the magnetospheric origin. At B
z
> 0, fluxes of harder (E > 1 keV) precipitating electrons were superimposed on the soft spectrum of precipitating particles in the equatorial part
of the red luminosity band. This red band part was hypothetically caused by the low-latitude boundary layer (LLBL) on closed
lines of the geomagnetic field, the estimated thickness of which is ∼3 R
e
. The 557.7 nm emission intensity increased during 3–5 min after SC/SI and was accompanied by the displacement of the red
band equatorward boundary toward lower latitudes. The displacement value was ∼150–200 km when the dynamic pressure abruptly
increased by a factor of 3–5. After SC/SI, the 630.0 nm emission intensity continued increasing during 16–18 min. It is assumed
that the time of an increase in the red line intensity corresponds to the time of saturation of the magnetospheric boundary
layers with magnetosheath particles after an abrupt increase in their density. 相似文献
12.
David A. Clague Jonathan T. Hagstrum Duane E. Champion Melvin H. Beeson 《Bulletin of Volcanology》1999,61(6):363-381
The tube-fed pāhoehoe lava flows covering much of the northeast flank of Kīlauea Volcano are named the 'Ailā'au flows. Their
eruption age, based on published and six new radiocarbon dates, is approximately AD 1445. The flows have distinctive paleomagnetic
directions with steep inclinations (40°–50°) and easterly declinations (0°–10°E). The lava was transported ∼40 km from the
vent to the coast in long, large-diameter lava tubes; the longest tube (Kazumura Cave) reaches from near the summit to within
several kilometers of the coast near Kaloli Point. The estimated volume of the 'Ailā'au flow field is 5.2±0.8 km3, and the eruption that formed it probably lasted for approximately 50 years. Summit overflows from Kīlauea may have been
nearly continuous between approximately AD 1290 and 1470, during which time a series of shields formed at and around the summit.
The 'Ailā'au shield was either the youngest or the next to youngest in this series of shields. Site-mean paleomagnetic directions
for lava flows underlying the 'Ailā'au flows form only six groups. These older pāhoehoe flows range in age from 2750 to <18,000
BP, and the region was inundated by lava flows only three times in the past 5000 years. The known intervals between eruptive
events average ∼1600 years and range from ∼1250 years to >2200 years. Lava flows from most of these summit eruptions also
reached the coast, but none appears as extensive as the 'Ailā'au flow field. The chemistry of the melts erupted during each
of these summit overflow events is remarkably similar, averaging approximately 6.3 wt.% MgO near the coast and 6.8 wt.% MgO
near the summit. The present-day caldera probably formed more recently than the eruption that formed the 'Ailā'au flows (estimated
termination ca. AD 1470). The earliest explosive eruptions that formed the Keanakāko'i Ash, which is stratigraphically above
the 'Ailā'au flows, cannot be older than this age.
Received: 10 October 1998 / Accepted: 12 May 1999 相似文献
13.
Şakir Şahin 《Journal of Seismology》2008,12(3):367-376
The seismic quality factor (Q
c) and the attenuation coefficient (δ) in the earth’s crust in southwest (SW) Anatolia are estimated by using the coda wave method based on the decrease of coda
wave amplitude by time on the seismogram. The quality factor Q
o, the value of Q
c at 1 Hz, and its frequency dependency η are determined from this method depending on the attenuation properties of scattered coda waves. δ is determined from the observations of amplitude variations of seismic waves. In applying the coda wave method, firstly,
a type curve representing the average pattern of the individual coda decay curves for 0.75, 1.5, 3.0, 6.0, 12.0, and 24.0 Hz
values was estimated. Secondly, lateral variation of coda Q and the attenuation coefficients for three main tectonic patterns
are estimated. The shape of the type curve is controlled by the scattering and attenuation in the crustal volume sampled by
the coda waves. The Q
o and η values vary from 30 to 180 and from 0.55 to 1.25, respectively for SW Anatolia. In SW Anatolia, coda Q–f relation is described by and δ = 0.008 km−1. These results are expected to help in understanding the degree of tectonic complexity of the crust in SW Anatolia. 相似文献
14.
The attenuation of coda waves is analysed for nine seismic stations in the area of convergent motion of the Adriatic microplate
and the Dinarides. The frequency dependent coda quality factor of the form Qc = Q0 fn is estimated for up to seven central frequencies (1.5, 3, 6, 9, 12, 18 and 24 Hz) and for 21 successive 30 s long time windows.
Q0 was found to increase from 68–353 for short lapse times of 20–50 s, to 158–373 for lapse times of 90–100 s. Parameter n is
observed to vary between 0.46 and 0.89, with a pronounced tendency to decrease with increasing Q0, and vice versa. Both Q0 and n seem to stabilize for lapse times larger than 50–80 s, indicating that a change in rock properties controlling coda
attenuation occurs at depths of about 100–160 km. The spatial distribution of observed Q0 is well correlated with observed seismicity and inferred tectonic activity. In particular, we observe significant negative
correlation of Q0 with the peak ground acceleration (PGA) estimate for the return period of 475 years. The degree of frequency dependence n,
is the smallest for stations on the islands, where the crust is the thinnest. The largest n is observed over the thickest
crust in the region, where the Moho lies at depths of over 55 km. 相似文献
15.
Charles R. Stern 《Bulletin of Volcanology》2008,70(4):435-454
For regionally widespread Holocene tephra layers in southernmost Patagonia, correlations based on both chemical and chronological
data indicate their derivation from five large-volume (>1 km3) explosive eruptions of four different volcanoes in the southernmost Andes. Bulk-tephra and tephra-glass major and trace-element
chemistry and Sr isotopic ratios unambiguously distinguish different source volcanoes, and imply that two of the regionally
widespread tephra (MB1 and MB2) were derived from Mt. Burney (52°S), one (R1) from Reclus (51°S), one (A1) from Aguilera (50°S) and one (H1) from Hudson volcano (46°S). The H1 tephra derived from the Hudson volcano, which is located at the southern end of the Andean Southern Volcanic Zone (SVZ; 33–46°S),
contains distinctive greenish andesitic glass with FeO > 4.5 wt.% and TiO2 > 1.2 wt.%. In contrast, rhyolitic glass in tephra derived from the eruptions of Mt. Burney, Reclus and Aguilera volcanoes,
which are located in the Andean Austral Volcanic Zone (AVZ; 49–55°S), is clear and transparent and has significantly lower
FeO and TiO2. Tephra derived from these three AVZ volcanoes all contain plagioclase, orthopyroxene, minor clinopyroxene and amphibole.
Biotite occurs only in the Aguilera A1 tephra, which also has the highest bulk-tephra and tephra-glass K2O and Rb contents. Averages of new and published 14C ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated
14C age of the R1 eruption of Reclus volcano to 12,685 ± 260 years BP, the MB1 and MB2 eruptions of Mt. Burney to 8,425 ± 500 and 3,830 ± 390 years BP, the Hudson H1 eruption to 6,850 ± 160 years BP, and the A1 eruption of Aguilera volcano to 3,000 ± 100 years BP. The volume of the largest of these eruptions, H1 of the Hudson volcano, is estimated as >18 km3. The volume of the Reclus R1 eruption is estimated at >10 km3, the Aguilera A1 eruption at between 4 and 9 km3, and the younger Mt. Burney MB2 eruption at ≥2.8 km3. The volume of the older MB1 Mt. Burney eruption is the least well constrained, but must have been larger than the younger MB2 eruption. The data indicate that the frequency of explosive activity of volcanic centers in the AVZ is lower than in the
southern SVZ. 相似文献
16.
We have collected 432 vertical component records from 45 stations of new CENC （China Earthquake Network Center） in Chinese mainland and adjacent regions. These records were used to calculate Q0 （Q at 1Hz） and η values of Lg coda from each station by the stack spectral ratio （SSR） method. Then the tomography method was applied to obtaining lateral variation of Q0 and η values in Chinese mainland and adjacent regions. The result indicates that Q0 value varies between 150 and 600 in the studied areas. Yunnan, southwest Sichuan, and northwest Myanmar show the lowest Q0 value （Q0〈240） and the crust of these regions is characterized by complicated crack and strong hydrothermal activity. The highest Q0 value （Qo〉510） exists in the border of southern Mongolia, Alxa and Ordos block. The η value varies between 0.45 and 0.75 in Chinese mainland and its adjacent regions. 相似文献
17.
Paleomagnetic characteristics of Carboniferous-Permian and Early Mesozoic geological complexes in Mongolia are studied. The studied rocks are shown to possess a multicomponent magnetization. Lowtemperature overprinting components of normal polarity discovered in nearly all of the studied strata were acquired after main deformation stages of the rocks, apparently in the Cenozoic. High-temperature overprinting components of reversed polarity identified in rocks of an active continental margin (ACM) were acquired when bimodal magma melts moved through ACM volcanic sequences. Late Carboniferous and Early Permian paleomagnetic poles of Mongolia calculated from directions of primary magnetization components are, respectively (Λ = 154.6, Φ = 32.2, A = 7.8) and (Λ = 95, Φ = 71, A = 8.7). Apparently, the territory of Mongolia in the Early Permian was a margin of the Siberian craton and was separated from the Northern China block by a basin extending for no less than 2000 km in the E-W direction. The strike of a marginal-continental volcanic belt was submeridional and a plate subducted under the continent from the east. Late Carboniferous-Permian intraplate magmatic complexes of Mongolia formed at various latitudes from various mantle sources during the northward movement of the Mongolian part of the Siberian continent. The oldest bimodal sequences of the Gobi-Tien Shan zone (318–314 Ma) formed at more southern latitudes (40°–47°–54°N) as compared with the 275-Ma complexes of the Gobi-Altai zone (51°–58°–67°N). Thus, sources of the Carboniferous-Permian intraplate magmatism in Central Asia either occupied a vast mantle region (up to 1000 km in the latitude direction) or moved together with the Asian continent. 相似文献
18.
19.
《Journal of Geodynamics》2008,45(3-5):129-148
The Andes between 36°30′ and 37°S represent a Cretaceous fold and thrust belt strongly reactivated in the late Miocene. Most of the features that absorbed Neogene shortening were already uplifted in the late Cretaceous, as revealed by field mapping and confirmed by previous fission track analysis. This Andean section is formed by two sectors: a western-inner sector generated by the closure of the upper Oligocene-lower Miocene intra-arc Cura Mallín basin between the middle and late Miocene (Guañacos fold and thrust belt), and an eastern-outer sector, where late Triassic-early Jurassic extensional depocenters were exhumed in two discrete phases of contraction, in the latest early Cretaceous and late Miocene to the Present, respectively (Chos Malal fold and thrust belt). Late Miocene deformation has not homogeneously reactivated Cretaceous compressive structures, being minimal south of 37°30′S through the eastern-outer sector (southern continuation of the Chos Malal fold and thrust belt). The reason for such an inhomogeneous deformational evolution seems to be related to the development of a late Miocene shallow subduction regime between 34°30′ and 37°45′S, as it was proposed in previous studies. This shallow subduction zone is evidenced by the eastward expansion of the arc that was accompanied by the eastern displacement of the orogenic front at these latitudes. As a result, the Cretaceous fold and thrust belt were strongly reactivated north of 37°30′S producing the major topographic break along the Southern Central Andes. 相似文献
20.
Rheological properties of the crust and upper mantle are essential data that are needed in modelling the mechanical behaviour of the shallow part of the earth. The importance of such data has been seen in discussions about the strength profile of continen… 相似文献