Crustal thickness and VP/VS variations in the Grenville orogen (Ontario, Canada) from analysis of teleseismic receiver functions

We have developed a simple semblance-weighted stacking technique to estimate crustal thickness and average V_P/V_S ratio using teleseismic receiver functions. We have applied our method to data from 32 broadband seismograph stations that cover a 700 × 400 km² region of the Grenville orogen, a 1.2–0.98 Ga Himalayan-scale collisional belt in eastern North America. Our seismograph network partly overlaps with Lithoprobe and other crustal refraction surveys. In 8 out of 9 cases where a crustal-refraction profile passes within 30 km of a seismograph station, the two independent crustal thickness estimates agree to within 7%. Our regional crustal-thickness model, constructed using both teleseismic and refraction observations, ranges between 34.0 and 52.4 km. Crustal-thickness trends show a strong correlation with geological belts, but do not correlate with surface topography and are far in excess of relief required to maintain local isostatic equilibrium. The thickest crust (52.4 ± 1.7 km) was found at a station located within the 1.1 Ga mid-continent (failed) rift. The Central Gneiss Belt, which contains rocks exhumed from deep levels of the crust, is characterized by V_P/V_S ranging from 1.78 to 1.85. In other parts of the Grenville orogen, V_P/V_S is found to be generally less than 1.80. The thinnest crust (34.5–37.0 km) occurs northeast of the 0.7 Ga Ottawa–Bonnechere graben and correlates with areas of high intraplate seismicity.     

Equation of state,structural behaviour and phase diagram of synthetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>, as a function of pressure and temperature

The behaviour of synthetic Mg-ferrite (MgFe₂O₄) has been investigated at high pressure (in situ high-pressure synchrotron radiation powder diffraction at ESRF) and at high temperature (in situ high-temperature X-ray powder diffraction) conditions. The elastic properties determined by the third-order Birch–Murnaghan equation of state result in K₀=181.5(± 1.3) GPa, K=6.32(± 0.14) and K= –0.0638 GPa^–1. The symmetry-independent coordinate of oxygen does not show significant sensitivity to pressure, and the structure shrinking is mainly attributable to the shortening of the cell edge (homogeneous strain). The lattice parameter thermal expansion is described by _a0+_a1*(T–298)+_a2/(T–298)², where _a0=9.1(1) 10^–6 K^–1, _a1=4.9(2) 10^–9 K^–2 and _a2= 5.1(5) 10^–2 K. The high-temperature cation-ordering reaction which MgFe-spinel undergoes has been interpreted by the ONeill model, whose parameters are = 22.2(± 1.8) kJ mol^–1 and =–17.6(± 1.2) kJ mol^–1. The elastic and thermal properties measured have then been used to model the phase diagram of MgFe₂O₄, which shows that the high-pressure transition from spinel to orthorombic CaMn₂O₄-like structure at T < 1700 K is preceded by a decomposition into MgO and Fe₂O₃.     

Vp/Vs ratio along the Vøring Margin, NE Atlantic, derived from OBS data: implications on lithology and stress field

A total of 13 regional Ocean Bottom Seismograph (OBS) profiles with an accumulated length of 2207 km acquired on the Vøring Margin, NE Atlantic have been travel time modelled with regards to S-waves. The V_p/V_s ratios are found to decrease with depth through the Tertiary layers, which is attributed to increased compaction and consolidation of the rocks. The V_p/V_s ratio in the intra-Campanian to mid-Campanian layer (1.75–1.8) in the central Vøring Basin is significantly lower than for the layers above and beneath, suggesting higher sand/shale ratio. This layer was confirmed by drilling to represent a layer of sandstone. This mid-Cretaceous ‘anomaly’ is also present in the northern Vøring Basin, as well as on the southern Lofoten Margin further north. The V_p/V_s ratio in the extrusive rocks on the Vøring Plateau is estimated to be 1.85, conformable with mafic (basaltic) rocks. Landward of the continent/ocean transition (COT), the V_p/V_s ratio in the layer beneath the volcanics is estimated to be 1.67–1.75. These low values suggest that this layer represents sedimentary rocks, and that the sand/shale ratio might be relatively high here. The V_p/V_s ratio in the crystalline basement is estimated to be 1.67–1.75 in the basin and on the landward part of the Vøring Plateau, indicating the presence of granitic/granodioritic continental crust. In the lower crust, the V_p/V_s ratio in the basin decreases uniformly from southwest to northeast, from 1.85–1.9 to 1.68–1.73, suggesting a gradual change from mafic (gabbroic) to felsic (granodioritic) lower crust. Significant (3–5%) azimuthal S-wave anisotropy is observed for several sedimentary layers, as well as in the lower crust. All these observations can be explained by invoking the presence of liquid-filled microcracks aligned vertically along the direction of the present day maximum compressive stress (NW–SE).     

The value ofC efor the Arabian Sea during summer monsoon

We estimate, from the moisture budget the bulk aerodynamic coefficient for latent heat flux (C _e) during the monsoon season over the central Arabian Sea. The average value ofC _eunder active monsoon conditions was found to be 2.25 × 10⁻³ which is nearly 60% higher than those previously used.     

Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard Margin west of Hornsund

The crustal structure along a 312 km transect, stretching from the axial mountains of the North Atlantic Knipovich Ridge to the continental shelf of Svalbard, has been obtained using seismic reflection data and wide angle OBS data. The resulting seismic V_p and V_s models are further constrained by a 2-D-gravity model. The principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow-spreading counterpart of the North Atlantic Ridge Systems. V_p is estimated to be 3.50–6.05 km/s for the upper oceanic crust (oceanic layer 2), with a marked increase away from the ridge. The measured V_p of 6.55–6.95 km/s for oceanic layer 3A and 7.10–7.25 km/s for layer 3B, both with a V_p/V_s ratio of 1.81, except for slightly higher values at the ridge axis, does not allow a clear distinction between gabbro and mantle-derived peridotite (10–40% serpentized). The thickness of the oceanic crust varies a lot along the transect from the minimum of 5.6 km to a maximum of 8.1 km. The mean thickness of 6.7 km for the oceanic crust is well above the average thickness for slow-spreading ridges (<10 mm/year half-spreading rate). The areas of increased thickness could be explained by large magma production-rates found in the zones of axial highs at the ridge axis, which also have generated the off-axial highs adjacent the ridge. We suggest that these axial and off-axial highs along the ridge control the lithological composition of the oceanic crust. This approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments (the axial and off-axial highs) and mantle-derived peridotite outside these zone.     

A study of turbulent characteristics of atmospheric boundary layer over monsoon trough region using Kytoon and Doppler sodar

As a part of the MONTBLEX-90 observational programme, Kytoon and Doppler sodar observations were taken at Kharagpur. These data are analysed to study the turbulent characteristics of the atmospheric boundary layer in terms of stability, temperature structure function (C _T ² ) and velocity structure function (C _v ² ).C _T ² follows aZ ^−4/3 law on most of the days, whereas the variation ofC _V ² is not systematic.C _V ² andC _T ² values are found to vary between 10⁻⁵−10⁻¹ m^4/3s⁻² and 10⁻⁵−10⁻²°C² m^−2/3 respectively.     

Composition of organic matter in subducted and unsubducted sediments off the Nicoya peninsula, Costa Rica (ODP Leg 170, Sites 1039 and 1040)

Investigation of sediment samples from Sites 1039 and 1040 (ODP Leg 170) drilled off the Nicoya peninsula (Costa Rica) by organic geochemical and organic petrological methods has revealed that subduction has only little influence on the composition of the sedimentary organic matter. Organic carbon contents reached 1.5% in the Pleistocene samples but Miocene and Pliocene sediments had an average organic carbon content of less than 0.5%. Organic carbon/sulfur ratios are generally below 2.8, reflecting an intense sulfate reduction in the uppermost sediments which was enhanced by sulfate supply both from sea water and deeper strata. Microscopical examinations indicate that the organic matter is mainly derived from marine sources. A small amount of terrigenous organic matter is, however, present as well according to n-alkane and fatty acid distributions. The alkenone unsaturation index U₃₇^k′ shows only a slight decrease during the Miocene and Pliocene, and stronger variations in the Pleistocene, probably indicating more stable sea surface temperatures during the Miocene and Pliocene. Variations in the Pleistocene can possibly be related to glacial/interglacial changes.     

High-T phase transition of synthetic ANaB(LiMg)CMg5Si8O22(OH)2 amphibole: an X-ray synchrotron powder diffraction and FTIR spectroscopic study

The synthetic amphibole Na_0.95(Li_0.95Mg_1.05)Mg₅Si₈O₂₂(OH)₂ was studied in situ at high-T, using IR OH-stretching spectroscopy and synchrotron X-ray powder diffraction. At room-T the sample has P2₁ /m symmetry, as shown by the FTIR spectrum. It shows in the OH region two well-defined and intense absorptions at 3,748 and 3,712 cm⁻¹, respectively, and two minor bands at 3,667 and 3,687 cm⁻¹. The main bands are assigned to the two independent O–H groups in the primitive structure. The two minor bands evidencing the presence of small amount of vacant A-site (^A□_0.05). With increasing T, these bands shift continuously and merge into a unique absorption at high temperature. A change as a function of increasing T is revealed by the evolution of the refined unit-cell parameters, whose trend shows a transition to C2/m at about 320–330°C. The spontaneous scalar strain, fitted with a tricritical 2–6 Landau potential, gives a T _c of 325(10)°C (β parameter = 0.27). Comparison with the second-order P2₁ /m ⇔ C2/m phase transition at 255°C for synthetic amphibole ^ANa_0.8^B(Na_0.8Mg_1.2)^CMg₅Si₈O₂₂(OH)₂ indicates that the substitution of Na with Li at the B-sites strongly affects the thermodynamic character and the T _c of the phase transition. The comparison of LNMSH amphiboles with cummingtonitic ones shows that the high-T thermodynamic behaviour is affected by A-site occupancy.     

点苍山-哀牢山杂岩带中北段嘎洒地区变沉积岩的成因矿物学与变质演化特征

点苍山-哀牢山变质杂岩带中北段嘎洒地区出露了多种典型的变沉积岩,其中夕线石榴黑云二长片麻岩和二云母片岩保存多期/多阶段矿物相转变特征,本文通过岩相学和矿物化学的综合分析,并结合传统矿物对温压计的估算结果,限定上述典型变沉积岩峰期角闪-麻粒岩相(M1)阶段、近等温减压-高温剪切变形阶段(M2)和晚期退变质(M3)阶段的矿物组合及变质温压条件。峰期角闪-麻粒岩相(M1)阶段的矿物组合为:石榴石(Grt)+板柱状夕线石(Sil1)+黑云母(Bt1)+钾长石(Kfs)+斜长石(Pl)+石英(Qtz)+钛铁矿(Ilm),变质温度压力条件为t=690~750℃,p=690~810 MPa;近等温减压-高温剪切变形阶段(M2)阶段,稳定矿物组合为:Grt+Sil2+Bt2+Kfs+Pl+Qtz+Ilm,黑云母在强烈走滑剪切作用下发生脱水熔融反应:2 Bt→Sil+6(Mg,Fe)O+K_2O+5 Qtz+2 H_2O,石榴石、黑云母和夕线石等受到剪切变形影响而发生强烈定向,形成的温度压力条件为t=650~720℃,p=450~630 MPa;晚期退变质阶段(M_3)的稳定矿物组合为:Qtz+Bt+Ms+Pl,退变的温度压力条件为t=580~640℃,p=400~500MPa。其变质演化p-T轨迹样式具有近等温减压的顺时针型式,表明点苍山-哀牢山变质杂岩带曾经历了一次明显的俯冲-碰撞造山事件,峰期变质可达到角闪-麻粒岩相;在碰撞后的构造折返过程中,上述变质岩石发生强烈的高温剪切变形作用,并伴随着黑云母等含水矿物的脱水熔融。     

Numerical analysis as applied to the environmental interpretation of carbonate microfacies of some sub-Himalayan carbonates (lower upper precambrian) in northwestern India

Forty-three samples of (1) Sirban Limestone of Riasi, Jammu and Kashmir State, India, based on six mineralogic and petrographic presence-absence variables, and (2) 36 samples of Bilaspur Limestone based on 11 presence-absence mineralogic and petrographic variables, were numerically classified by Q-mode cluster analysis using Sokal and Michner's Simple Matching Coefficient. Sirban Limestone of Riasi yielded 10 clusters or groups indicating four depositional environments: (1) intertidal, (2) intertidal to subtidal, (3) subtidal, and (4) deep-water basinal. Similarly, Bilaspur Limestone yielded nine clusters indicative of the same four environments. A Q-mode ordination of the Riasi samples and of Bilaspur Limestone shows a generalized shelf-to-basin carbonate deposition profile. Results of this study substantiate earlier conclusions of Rao (1979) based on field, mineralogic, and petrographic study of the above-mentioned carbonates.     

吉林南部辉南-靖宇地区岩石圈地幔氧化-还原状态及研究意义

吉林省南部辉南-靖宇地区第四纪碱性玄武岩中的地幔包体主要为尖晶石相二辉橄榄岩和方辉橄榄岩。二辉橄榄岩和方辉橄榄岩的平衡温度分别为770~1000℃和850~1025℃,对应的氧逸度 (f_O2)值分别为FMQ -0.70至+0.34 (均值为FMQ -0.06) 和FMQ -0.46至+0.05 (均值为FMQ -0.15),它们与深海橄榄岩(abyssal peridotites)以及软流圈地幔的f_O2相似。橄榄岩的f_O2值,连同其全岩化学成分(如Mg^#、Al₂O₃、CaO、Ni、Co和Cr)和矿物化学成分(如橄榄石的Fo、尖晶石的Cr^#和Mg^#,以及辉石的Mg^#)特征,表明辉南-靖宇地区龙岗火山群下面的岩石圈地幔很可能是在晚中生代以来,伴随着华北克拉通和扬子板块的碰撞以及来自东侧太平洋板块和北侧蒙古-额霍次克(Mongolo-Okhotsk)板块分别向西和向南的俯冲叠加,原来的古老岩石圈失衡、塌陷(拆沉？),取而代之的深部软流圈底辟、上涌,又经历了低度部分熔融的产物。     

Seismic hazard in mega city Kolkata, India

The damages caused by recent earthquakes in India have been a wake up call for people to take proper mitigation measures, especially the major cities that lie in the high seismic hazard zones. Kolkata City, with thick sediment deposit (∼12 km), one of the earliest cities of India, is an area of great concern as it lies over the Bengal Basin and lies at the boundary of the seismic zones III and IV of the zonation map of India. Kolkata has been affected by the 1897 Shillong earthquake, the 1906 Calcutta earthquake, and the 1964 Calcutta earthquake. An analysis on the maximum magnitude and b-value for Kolkata City region is carried out after the preparation of earthquake catalog from various sources. Based on the tectonic set-up and seismicity of the region, five seismic zones are delineated, which can pose a threat to Kolkata in the event of an earthquake. They are broadly classified as Zone 1: Arakan-Yoma Zone (AYZ), Zone 2: Himalayan Zone (HZ), Zone 3: Shillong Plateau Zone (SPZ), Zone 4: Bay of Bengal Zone (BBZ), and Zone 5: Shield Zone (SZ). The maximum magnitude (m _max) for Zones 1, 2, 3, 4, and 5 are 8.30 ± 0.51, 9.09 ± 0.58, 9.20 ± 0.51, 6.62 ± 0.43 and 6.61 ± 0.43, respectively. A probability of 10% exceedance value in 50 years is used for each zone. The probabilities of occurrences of earthquakes of different magnitudes for return periods of 50 and 100 years are computed for the five seismic zones. The Peak Ground Acceleration (PGA) obtained for Kolkata City varies from 0.34 to 0.10 g.     

Reconstructing the migration patterns of late Pleistocene mammals from northern Florida, USA

We used analyses of the strontium isotope (⁸⁷Sr/⁸⁶Sr) ratios of tooth enamel to reconstruct the migration patterns of fossil mammals collected along the Aucilla River in northern Florida. Specimens date to the late-glacial period and before the last glacial maximum (pre-LGM). Deer and tapir displayed low ⁸⁷Sr/⁸⁶Sr ratios that were similar to the ratios of Florida environments, which suggest that these taxa did not migrate long distance outside of the Florida region. Mastodons, mammoths, and equids all displayed a wide range of ⁸⁷Sr/⁸⁶Sr ratios. Some individuals in each taxon displayed low ⁸⁷Sr/⁸⁶Sr ratios that suggest they ranged locally, while other animals had high ⁸⁷Sr/⁸⁶Sr ratios that suggest they migrated long distances (> 150 km) outside of the Florida region. Mastodons were the only taxa from this region that provided enough well-dated specimens to compare changes in migration patterns over time. Pre-LGM mastodons displayed significantly lower ⁸⁷Sr/⁸⁶Sr ratios than late-glacial mastodons, which suggests that late-glacial mastodons from Florida migrated longer distances than their earlier counterparts. This change in movement patterns reflects temporal changes in regional vegetation patterns.     

n-alkane distribution coupled with organic carbon isotope composition in the shell bar section, Qarhan paleolake, Qaidam basin, NE Tibetan Plateau

Lipids extracted from lacustrine deposits in the paleolake Qarhan of the Qaidam basin in the northeastern Tibetan Plateau were determined by conventional gas chromatography-mass spectrometry. Several series of biomarkers were identified, mainly including n-alkanes, n-alkan-2-ones, n-alkanoic acids, branched alkanes, triterpenoids and steroids, indicative of various biogenic contributions. On the basis of cluster analysis, the n-C₁₅, n-C₁₇, n-C₁₉ alkanes were proposed to be derived from algae and/or photosynthetic bacteria, the n-C₂₁, n-C₂₃, n-C₂₅ homologues from aquatic plants, and the n-C₂₉, n-C₃₁ homologues from vascular plants. In contrast, the n-C₂₇ alkane is not categorized in the n-C₂₉ and n-C₃₁ group of alkanes, probably due to more complex origins including both aquatic and vascular plants, and/or differential biodegradation. Stratigraphically, layers-2, 4 and 5 were found to show a close relationship in n-alkane distribution, associated with a positive shift in carbon isotope composition of bulk organic matter (δ¹³C_org), inferring a cold/dry period. Layers-1 and 6 were clustered together in association with a negative δ¹³C_org, excursion, probably indicating a relatively warm/humid climate. The potential coupling between the n-alkane distributions and δ¹³C_org, suggests a consequence of vegetation change in response to climate change, with the late MIS3 being shown to be unstable, thought to be the climatic optimum in the Tibetan Plateau. Our results suggest that the cluster analysis used in this study probably provides an effective and authentic method to investigate the n-alkane distribution in paleolake sediments.     

Application of the Dynamic Cone Penetrometer (DCP) for determination of the engineering parameters of sandy soils

Determination of the in situ engineering properties of foundation materials has always been a challenge for geotechnical engineers and, thus, several methods have been developed so far. Dynamic Cone Penetration (DCP) test is one of the most versatile amongst them. In the present research, a light weight simple DCP device was developed and used for evaluation of the engineering properties of sandy soils in laboratory conditions. The device consisted of an 8-kg hammer that drops over a height of 575 mm, and drives a 60° cone tip with 20 mm base diameter into the ground. To control the validation of the results, laboratory direct shear and plate load tests were used as reference tests. The soil sample was a poorly graded sandy soil (SP) taken from alluvial deposits of the Tehran plain. All DCP tests and PLTs were undertaken on compacted soil in a mould with 700 mm diameter and 700 mm height. Based on the results of the experiments, the relationships between Dynamic Penetration Index (DPI), relative density (D_r), modulus of elasticity (E), shear modulus (G), modulus of subgrade reaction (K_S), and the friction angle of the soil were obtained with a high coefficient of determination (> 90%). The repeatability of the test results was also evaluated by calculating the coefficient of variations (C_v), which was less than 30% for all tests.     

Lithospheric structure of the Tornquist Zone resolved by nonlinear P and S teleseismic tomography along the TOR array

The main aim of the TOR project is to study the lithospheric–asthenospheric boundary structure under the Sorgenfrei–Tornquist Zone, across northern Germany, Denmark and southern Sweden. Relative arrival-time residuals of teleseismic P and S phases from 51 earthquakes, recorded by 150 seismic stations along the TOR array, were used to delineate the transition zone in the studied area. The effects of crustal structures were investigated by correcting the teleseismic residuals for travel-time variations in the crust based on a 3D crustal model derived from other data. The inversion was carried out for S phases. The results were then compared with the corresponding P-wave models. As expected, the derived models show that the relatively old and cold Baltic Shield has higher velocity at depth than the younger lithosphere farther South. The models show two sharp and distinct increases in depth to velocities which are low compared to our reference model, as we move from South to North. The location and sharpness of these boundaries suggests that the features resolved are, at least partially, compositional in origin, presumably related to mantle depletion. A sharp and steep subcrustal boundary is found roughly coincident with the southern edge of Sweden. This is below where the edge of the Baltic Shield is usually placed, based on surface geological evidence (the Sorgenfrei–Tornquist Zone). Another less significant transition is recognised more or less beneath the Elbe-lineament. Relatively high d(V_p / V_s) ratios under the central part of the profile (Denmark) indicate relatively low S-velocity in an area where a gravity high supports the hypothesis of extensive mafic intrusions.     

松辽盆地营城组火山岩储层流动单元特征和控制因素

根据孔隙度、渗透率、储层品质指数(RQI)、流动层带指数(FZI)4个参数对XS1井区白垩系营城组火山岩的388个样品进行聚类分析,通过对聚类结果与各井产气情况的对比将储层流动单元划分为4类,所占比例依次为39.2%(Ⅲ类)、33.2%(Ⅱ类)、25.0%(Ⅰ类)、2.6%(Ⅳ类)。Ⅰ类储层流动单元多为高孔高渗、高孔中渗和中孔高渗储层,厚度范围为10～20m;Ⅱ类储层流动单元多为中孔高渗、高孔中渗和低孔高渗储层,厚度范围为10～47m;Ⅲ类储层流动单元多为中孔高渗、中孔低渗和低孔中渗储层,厚度范围为11～86m;Ⅳ类储层流动单元为低孔低渗和特低孔特低渗储层,厚度小于10m。火山岩储层流动单元发育和分布受火山机构相带和火山岩亚相的控制,表现为火山口-近火山口相带成为Ⅰ、Ⅱ类储层流动单元的机率最大,近源相带成为Ⅱ、Ⅲ类储层流动单元的机率最大,远源相带成为Ⅲ类和Ⅳ类储层流动单元的机率最大。原生气孔发育的上部亚相和粒间孔发育的热碎屑流亚相形成Ⅰ类储层流动单元的机率最大,原生孔隙不发育的空落亚相和下部亚相形成Ⅲ类储层流动单元的机率大。实现了火山岩储层流动单元的单井识别,为其三维模型的建立提供依据。     

2022年1月8日青海门源MS 6.9地震地表破裂考察的初步结果及对冷龙岭断裂活动行为和区域强震危险性的启示

2022年1月8日青海门源M_S 6.9地震发生在青藏高原东北缘的祁连山断块内部,仪器震中位于海原活动断裂系西段的冷龙岭断裂带上,是该断裂系自1920年海原8.5级大地震后再次发生M>6.5的强震。考察结果的初步总结表明,此次门源地震产生了呈左阶斜列分布、总长度近23 km的南北两条破裂,在两者之间存在长约3.2 km、宽近2 km的地表破裂空区。南支破裂(F₁)出现在托来山断裂的东段,走向91°,长约2.4 km,以兼具向南逆冲的左旋走滑变形为主,最大走滑位移近0.4 m。北支主破裂(F₂)出现在冷龙岭断裂的西段,总长度近20 km,以左旋走滑变形为主,呈整体微凸向北东的弧形展布,包含了走向分别为102°、109°和118°的西、中、东三段,最大走滑位移出现在中段,为3.0±0.2 m。此外,在北支主破裂中—东段的北侧新发现一条累计长度约7.6 km、以右旋正断为主的北支次级破裂(F₃),累计最大走滑量约0.8 m,最大正断位移约1.5 m。综合分析认为,整个同震破裂以左旋走滑变形为主,具有双侧破裂特点,宏观震中位于北支主破裂的中段,其地表走滑位移很大可能与震源破裂深度浅有关,其中的右旋正断次级破裂可能是南侧主动盘向东运移过程中拖曳北侧块体发生差异运动所引起的特殊变形现象。印度与欧亚板块近南北向强烈碰撞挤压导致南祁连断块沿海原左旋走滑断裂系向东挤出,从而引发该断裂系中的托来山断裂与冷龙岭断裂同时发生破裂,成为导致此次强震的主要动力机制。在此大陆动力学背景下,以海原左旋走滑断裂系为主边界的祁连山断块及其周边的未来强震危险性需得到进一步重视。