Comparison between the Chile and Mexico triple junction areas substantiates slab window development beneath northwestern Mexico during the past 12-10 Myr

When combined with the Miocene-Recent volcanic record of Baja California, a parallel drawn between the Chile and Mexico triple junction areas substantiates slab window development beneath northwestern Mexico during the past 12-10 Myr. The slab-free zone manifestations challenge the notion that ridge subduction has not occurred beneath the southern Baja California peninsula. The geochemically distinctive rocks from the Santa Clara volcanic field of west-central Baja California, including coeval adakites and niobium-enriched basalt, are commonly inferred to signal partial melting of the subducting plate at shallow depths and relatively high temperatures, before slab dehydration occurs. Such PT conditions for slab melting have only been observed in association with spreading-ridge subduction. We propose that slab window development beneath southern Baja California and mainland Mexico (30° to 18°N) resulted from subduction of the East Pacific rise.     

Latent heat effects of the major mantle phase transitions on low-angle subduction

Very low to zero shallow dip angles are observed at several moderately young subduction zones with an active trenchward moving overriding plate. We have investigated the effects of latent heat for this situation, where mantle material is pushed through the major mantle phase transitions during shallow low-angle subduction below the overriding plate. The significance of the buoyancy forces, arising from the latent heat effects, on the dynamics of the shallowly subducting slab is examined by numerical modeling. When a 32-Ma-old slab is overridden with 2.5 cm/yr by a continent, flat subduction occurs with a 4–5 cm/yr convergence rate. When latent heat is included in the model, forced downwellings cause a thermal anomaly and consequently thermal and phase buoyancy forces. Under these circumstances, the flat slab segment subducts horizontally about 350 km further and for about 11 Ma longer than in the case without latent heat, before it breaks through the 400-km phase transition. The style of subduction strongly depends on the mantle rheology: increasing the mantle viscosity by one order of magnitude can change the style of subduction from steep to shallow. Similarly, an overriding velocity of less than 1 cm/yr leads to steep subduction, which gradually changes to flat subduction when increasing the overriding velocity. However, these model parameters do not change the aforementioned effect of the latent heat, provided that low-angle subduction occurs. In all models latent heat resulted in a substantial increase of the flat slab length by 300–400 km. Varying the olivine–spinel transition Clapeyron slope γ from 1 to 6 MPa/K reveals a roughly linear relation between γ and the horizontal length of the slab. Based on these results, we conclude that buoyancy forces due to latent heat of phase transitions play an important role in low-angle subduction below an overriding plate.     

汤加—克马德克俯冲带现今非均匀应力场特征及其动力学意义

汤加—克马德克俯冲带是太平洋板块向澳大利亚板块俯冲碰撞的动力作用区,是全球俯冲带动力学研究的热点区域.本研究基于EHB地震目录,对汤加—克马德克俯冲带(18.5°S—28.5°S)区域进行平面拟合,得到该范围内俯冲带走向约为196°,倾角约为48°;利用该俯冲带研究区域内Global CMT目录,对不同位置、不同深度进行区域应力张量反演,得到汤加—克马德克俯冲带研究区内精细的应力图像.结果显示:(1)俯冲带浅部(60~300km)应力结构非均匀特征明显,主应力轴倾伏角变化多样,并且最大主压应力轴方位在24°S左右发生明显偏转,我们推测这可能与洋底构造路易斯维尔海链俯冲有关;(2)中部(300~500km)最大主压、主张应力轴由北向南逐渐发生偏转,这可能与由北向南流动的地幔流对俯冲板片产生推挤作用有关,并且这种推挤作用向南逐渐减弱;(3)深部(500~700km)最大主压应力轴沿俯冲方向分布;(4)本文的结果还发现了主俯冲带深部西侧"偏移"板片与主俯冲带应力结构不同,表明"偏移"板片与主俯冲带是分离的.     

西北太平洋俯冲带日本本州至中国东北段应力场反演

本研究基于Global CMT提供的1196个1976年11月—2017年1月MW4.6地震矩心矩张量解,对西北太平洋俯冲带日本本州至中国东北段的应力场进行反演计算,得到了从浅表到深部俯冲带应力状态的完整分布.结果显示:俯冲带浅表陆壳一侧应力场呈现水平挤压、垂向拉伸状态,洋壳一侧的应力状态则相反,即近水平拉张、近垂向压缩.沿着俯冲板片向下,应力主轴逐渐向俯冲板片轮廓靠拢,其中位于双地震层(120km深度附近)之上的部分,主张应力轴沿俯冲板片轮廓展布而又比其更为陡倾;双地震层内的应力模式同典型I型双层地震带内的应力模式一致,即上层沿俯冲板片轮廓压缩、下层沿俯冲板片轮廓拉伸;双地震层之下,应力模式逐步转变为主压应力轴平行于俯冲板片轮廓.通观所研究的整个俯冲系统,水平面内主压和主张应力轴基本保持了与西北太平洋板片俯冲方向上的一致性,同经典俯冲板片的应力导管模型所预言的俯冲带应力模式相符;而主张应力轴在俯冲板片表面之下的中源地震深度范围内转向海沟走向,或许同研究区域横跨日本海沟与千岛海沟结合带,改变的浅部海沟形态致使完整俯冲板片下部产生横向变形有关.     

板块俯冲中水分运移过程及其地球物理含义

流体/水分在地球演化过程中具有重要作用,它的存在可以提高地质体的扩散及蠕变,降低岩石/地幔的固液相限,对地质体的地球物理性质、地质灾害诱发、地质构造演化等都有着重要的作用.在板块俯冲区,流体/水分的影响贯穿了整个动力学过程,但板块深部脱水还存在着争议,且目前系统地研究水分在整个俯冲中的迁移过程及其地球物理意义的工作还较...     

Subduction of continental margins and the uplift of high-pressure metamorphic rocks

The mechanism by which high-pressure metamorphosed continental material is emplaced at high structural levels is a major unsolved problem of collisional orogenesis. We suggest that the emplacement results from partial subduction of the continental margin which, because of its high flexural rigidity, produces a rapid change in the trajectory of the descending slab. We assume a two-fold increase in effective elastic thickness of the lithosphere as the continental margin approaches the subduction zone, and calculate the flexural profile of a thin plate for progressive downward migration of the zone of increased rigidity. We assess the effect of changes in the flexural profile on the overlying accretionary prism and mantle wedge as the continent approaches by estimating the extra stresses that are imposed on the wedge due to the bending moment exerted by the continental part of the plate. The wedges overlying the subduction zones, and the subducting slab itself, experience substantial extra compressional stress at depths of around 100 km, and extensional stress at shallower depths, as the continental margin passes through the zone of maximum curvature. The magnitudes of such extra stresses are probably adequate to effect significant deformation of the wedge and/or the descending plate, and are experienced in a time interval of less than 5 m.y. for typical subduction rates. The spatial variation of yield stresses in the region of the wedge and descending slab indicates that much of this deformation may be taken up in the crustal part of the descending slab, which is the weakest region in the deeper parts of the subduction zone. This may result in rapid upward migration of the crust of the partially subducted continental margin, against the flow of subduction. High-pressure metamorphosed terranes emplaced by the mechanism envisaged in this paper would be bounded by thrust faults below and normal faults above. Movement on the faults would have been coeval, and would have resulted in rapid unroofing of the high-pressure terranes, synchronous with arrival of the continental margin at the subduction zone and, therefore, relatively early in the history of a collisional orogen.     

Global shear stress pattern in main seismic active belts

ＧｌｏｂａｌｓｈｅａｒｓｔｒｅｓｐａｔｅｒｎｉｎｍａｉｎｓｅｉｓｍｉｃａｃｔｉｖｅｂｅｌｔｓＬＥＩＸＩＡＯ（肖磊）ＰＥＩ－ＳＨＡＮＣＨＥＮ（陈培善）ＩｎｓｔｉｔｕｔｅｏｆＧｅｏｐｈｙｓｉｃｓ，ＳｔａｔｅＳｅｉｓｍｏｌｏｇｉｃａｌＢｕｒｅａｕ，Ｂｅｉ...     

Effects of relative plate motion on the deep structure and penetration depth of slabs below the Izu-Bonin and Mariana island arcs

An increasing number of seismological studies indicate that slabs of subducted lithosphere penetrate the Earth's lower mantle below some island arcs but are deflected, or, rather, laid down, in the transition zone below others. Recent numerical simulations of mantle flow also advocate a hybrid form of mantle convection, with intermittent layering. We present a multi-disciplinary analysis of slab morphology and mantle dynamics in which we account explicitly for the history of subduction below specific island arcs in an attempt to understand what controls lateral variations in slab morphology and penetration depth. Central in our discussion are the Izu-Bonin and Mariana subduction zones. We argue that the differences in the tectonic evolution of these subduction zones—in particular the amount and rate of trench migration—can explain why the slab of subducted oceanic lithosphere seems to be (at least temporarily) stagnant in the Earth's transition zone below the Izu-Bonin arc but penetrates into the lower mantle below the Mariana arc. We briefly speculate on the applicability of our model of the temporal and spatial evolution of slab morphology to other subduction zones. Although further investigation is necessary, our tentative model shows the potential for interpreting seismic images of slab structure by accounting for the plate-tectonic history of the subduction zones involved. We therefore hope that the ideas outlined here will stimulate and direct new research initiatives.     

不同类型俯冲带地震竖向地震动阻尼修正系数对比研究

俯冲带地区竖向地震动的阻尼修正系数在工程结构抗震设计中起着重要作用。由于俯冲带地区的板块构造复杂,俯冲带地区的地震可划分为浅壳上地幔地震、板内地震和板间地震3种类型。为研究不同类型俯冲带地震的竖向地震动阻尼修正系数间是否具有显著差异而需要分别建立不同的阻尼修正系数模型,采用日本俯冲带地区的地震动数据,通过假设检验和构造差异指标的方式对不同类型地震的竖向加速度和位移反应谱的阻尼修正系数进行两两比较。结果显示:不同地震类型的竖向地震动阻尼修正系数在众多谱周期上存在统计意义和工程实际意义上的显著差异。该研究表明:研究俯冲带地区竖向地震动阻尼修正系数时需要考虑地震类型的影响。     

Relocation of shallow earthquakes in southern Alaska using Joint Hypocenter Determination method

A subset of 2660 shallow earthquakes (0–50 km) that occurred from 1988 to 1996 in south central Alaska between 155°W and 145°W and 59°N and 63°N was relocated using the joint hypocenter determination (JHD) method. Both P- and S-wave observations recorded by the regional seismic network were used. Events were relocated in twenty different groups based on their geographic location and depth using two velocity models. As a result of the relocation, the majority of the hypocenters shifted downward, while the epicenter locations did not change significantly. The distribution of the shallow subduction zone earthquakes indicates the existence of two seismically independent blocks, with one block occupying the northeastern part and the other occupying the central and western parts of the study area. The boundary between the blocks is marked by a 15 to 20 km wide seismicity gap to the southeast of 149.5°W and 62°N. The analysis of the fault plane solutions for shallow subduction zone earthquakes shows that an overwhelming majority of the solutions represent normal, oblique-normal or strike-slip faulting with predominant WNW-ESE orientation of T-axes. This indicates a down-dip extensional regime for the subducting slab at shallow depths. Very few earthquakes yielded fault plane solutions consistent with thrusting on a contact zone between the overriding and subducting plates. This result may be an indication that currently either the strain energy is not released at the contact zone or it is associated with aseismic motion.     

基于三重震相波形非线性反演的俯冲带410-km间断面起伏研究

利用NECESSArray宽频带地震台阵记录的P波三重震相波形资料,采用遗传算法,对千岛俯冲板块内部及附近410-km间断面的结构进行了非线性反演.其中,选取了发生在俯冲带的发震时刻为2009年10月10日21时24分(GMT时间)震级为M_w5.9的地震;其三重震相的射线回折点处射线路径的方向与俯冲板块的走向大致一致,克服了间断面在俯冲板块内部沿俯冲方向起伏剧烈、不易识别的困难,设计以震中为顶点、方位角范围分别为275°～280°、269°～274°、264°～266°的北、中、南三个扇形区域,用于研究410-km间断面逐渐靠近俯冲板块直至处在其中的起伏情况;"先对齐、后反演"的具体计算方案极大地减小了浅部结构不确定性对反演结果的影响;同时,整体归一化策略充分利用了台阵的振幅信息,有效地加强了对深部结构的约束.反演结果显示,"410-km间断面"在北区抬升了10～20 km,在中区抬升了20～30 km,在南区抬升了60～70 km,与橄榄石-瓦兹利石平衡态相变界面的矿物物理学预测结果一致;其波速跃变在北区为10%,在中区为10%,在南区为7%.扣除了前人在层析成...     

Kamchatka subduction zone,May 2013: the Mw 8.3 deep earthquake,preceding shallow swarm and numerous deep aftershocks

A sequence of 98 teleseismically recorded earthquakes occurred off the east coast of Kamchatka at depths between 10-90 km around latitude 52.5°N and longitude 160°E on May 16–23, 2013. The swarm occurred along the northern limit of the rupture area of the 1952 M_w 9.0 great Kamchatka earthquake, the fifth largest earthquake in the history of seismic observations. On May 24, 2013 the strongest deep earthquake ever recorded of M_w 8.3 occurred beneath the Sea of Okhotsk at a depth of 610 km in the Pacific slab of the Kamchatka subduction zone, becoming the northernmost deep earthquake in the region. The deep M_w 8.3 earthquake occurred down-dip of the shallow swarm in a transition zone between the southern deep and northern shallow segments of the Pacific slab. Several deep aftershocks followed, covering a large, laterally elongated part of the slab. We suppose that the two described earthquake sequences, the May 16–23 shallow earthquake swarm and the May 24–28 deep mainshock-aftershock series, represent a single tectonic event in the Pacific slab having distinct properties at different depth levels. A low-angle underthrusting of the shallow part of the slab recorded by the shallow earthquake swarm activated the deep part; this process induced the deep mainshock-aftershock series only three days after the swarm. The domain of the subducting slab activated by the May 2013 earthquake occurrence was extraordinarily large both down-dip and along-strike.     

Where and why do large shallow intraslab earthquakes occur?

We try to find how often, and in what regions large earthquakes (M≥7.0) occur within the shallow portion (20-60 km depth) of a subducting slab. Searching for events in published individual studies and the Harvard University centroid moment tensor catalogue, we find twenty such events in E. Hokkaido, Kyushu-SW, Japan, S. Mariana, Manila, Sumatra, Vanuatu, N. Chile, C. Peru, El Salvador, Mexico, N. Cascadia and Alaska. Slab stresses revealed from the mechanism solutions of these large intraslab events and nearby smaller events are almost always down-dip tensional. Except for E. Hokkaido, Manila, and Sumatra, the upper plate shows horizontal stress gradient in the arc-perpendicular direction. We infer that shear tractions are operating at the base of the upper plate in this direction to produce the observed gradient and compression in the outer fore-arc, balancing the down-dip tensional stress of the slab. This tectonic situation in the subduction zone might be realized as part of the convection system with some conditions, as shown by previous numerical simulations.     

三维板块几何形态对大陆深俯冲动力学的制约

大陆深俯冲及超高压变质作用是大陆动力学的重要研究内容,前人进行了系统的地质、地球物理观测以及数值模拟研究.然而,自然界中大陆板块的俯冲、碰撞及造山过程大部分具有明显的沿走向的差异性,这种典型的三维特征可能很大程度上依赖于会聚大陆板块的初始几何学和运动学特征.本文采用三维高分辨率的动力学数值模拟方法,建立了方形大陆板块和楔形大陆板块两种不同的俯冲-碰撞模型,并且俯冲大陆板块侧面与大洋俯冲带相邻.数值模拟结果揭示大洋板块可以持续地俯冲到地幔之中,而大陆板块俯冲到一定深度处,其前端的俯冲板块将发生断离,并进而造成残余的大陆板块俯冲角度的减小.方形大陆俯冲板块的断离深度约为150km,而楔形大陆俯冲板块的断离深度较大,约250~300km,这很大程度上取决于俯冲带中大洋板块的牵引力和大陆板块的负浮力之间的竞争关系.同时,无论方形还是楔形大陆板块俯冲模型中,板块断离后,侧向的大洋俯冲板块仍可以拖曳约60~70km宽的大陆边缘岩石圈持续向下俯冲,揭示了新西兰东部的洋-陆空间转换俯冲带的动力学机制.并且,数值模型与喜马拉雅造山带和秦岭—大别—苏鲁造山带进行了对比,进而对其高压-超高压岩石空间展布沿走向的差异性特征和机制提供了一定的启示.     

宽频带海底地震仪的地震重定位对马尼拉俯冲板片形态的约束

将宽频带OBS用于海底天然地震长期观测,在国内尚处于实验阶段.2015年在马尼拉俯冲带北段开展了为期6个月的宽频带海底天然地震观测试验.根据回收的1台海底地震仪(OBS04)与国际地震台网的718台陆地地震台站,共记录到7562个P波走时和5002个S波走时数据,利用Hyposat地震定位方法,对马尼拉俯冲带北部(119°E—123°E,19°N—22°N)在2015年8月至2016年2月期间的264个地震进行了重定位.地震重定位的结果及定位误差分析表明,在海域布设的OBS04台站让地震观测的空间分布更为合理,提高了地震定位精度;重定位后的震中分布更为集中,与地质构造吻合良好;浅部的地震活动较为活跃,分布密集,与浅部断层发育有关;重定位后的4条震源深度投影剖面,从不同角度较好地约束了俯冲板片上边界的板片形态,板片倾角在浅部0～30km区间约为10°～22°,随着深度的增加,俯冲板片逐渐变陡,在深度120～180km处倾角约为41°～58°.该项研究为马尼拉俯冲带北段的板片形态提供了重要约束,而且为今后长期天然地震观测提供了重要而宝贵的经验与借鉴.     

On the origin of El Chichón volcano and subduction of Tehuantepec Ridge: A geodynamical perspective

The origin of El Chichón volcano is poorly understood, and we attempt in this study to demonstrate that the Tehuantepec Ridge (TR), a major tectonic discontinuity on the Cocos plate, plays a key role in determining the location of the volcano by enhancing the slab dehydration budget beneath it. Using marine magnetic anomalies we show that the upper mantle beneath TR undergoes strong serpentinization, carrying significant amounts of water into subduction. Another key aspect of the magnetic anomaly over southern Mexico is a long-wavelength (∼ 150 km) high amplitude (∼ 500 nT) magnetic anomaly located between the trench and the coast. Using a 2D joint magnetic-gravity forward model, constrained by the subduction P–T structure, slab geometry and seismicity, we find a highly magnetic and low-density source located at 40–80 km depth that we interpret as a partially serpentinized mantle wedge formed by fluids expelled from the subducting Cocos plate. Using phase diagrams for sediments, basalt and peridotite, and the thermal structure of the subduction zone beneath El Chichón we find that ∼ 40% of sediments and basalt dehydrate at depths corresponding with the location of the serpentinized mantle wedge, whereas the serpentinized root beneath TR strongly dehydrates (∼90%) at depths of 180-200 km comparable with the slab depths beneath El Chichón (200-220 km). We conclude that this strong deserpentinization pulse of mantle lithosphere beneath TR at great depths is responsible for the unusual location, singularity and, probably, the geochemically distinct signature (adakitic-like) of El Chichón volcano.     

Dynamics of thinning and destruction of the continental cratonic lithosphere: Numerical modeling

Thinning of the cratonic lithosphere is common in nature, but its destruction is not. In either case, the mechanisms for both thinning and destruction are still widely under debate. In this study, we have made a review on the processes and mechanisms of thinning and destruction of cratonic lithosphere according to previous studies of geological/geophysical observations and numerical simulations, with specific application to the North China Craton (NCC). Two main models are suggested for the thinning and destruction of the NCC, both of which are related to subduction of the oceanic lithosphere. One is the “bottom-up” model, in which the deeply subducting slab perturbs and induces upwelling from the hydrous mantle transition zone (MTZ). The upwelling produces mantle convection and erodes the bottom of the overriding lithosphere by the fluid-melt-peridotite reaction. Mineral compositions and rheological properties of the overriding lithospheric mantle are changed, allowing downward dripping of lithospheric components into the asthenosphere. Consequently, lithospheric thinning or even destruction occurs. The other is the “top-down” model, characterized by the flat subduction of oceanic slab beneath the overriding cratonic lithosphere. Dehydration reactions from the subducting slab would significantly hydrate the lithospheric mantle and decrease its rheological strength. Then the subduction angle may be changed from shallow to steep, inducing lateral upwelling of the asthenosphere. This upwelling would heat and weaken the overriding lithospheric mantle, which led to the weakened lithospheric mantle dripping into the asthenosphere. These two models have some similarities, in that both take the subducting oceanic slab and relevant fluid migration as the major driving mechanism for thinning or destruction of the overriding cratonic lithosphere. The key difference between the two models is the effective depth of the subducting oceanic slab. One is stagnation and flattening in the MTZ, whereas the other is flat subduction at the bottom of the cratonic lithosphere. In the NCC, the eastern lithosphere was likely affected by subduction of the Izanagi slab during the Mesozoic, which would have perturbed the asthenosphere and the MTZ, and induced fluid migration beneath the NCC lithosphere. The upwelling fluid may largely have controlled the reworking of the NCC lithosphere. In order to discuss and analyze these two models further, it is crucial to understand the role of fluids in the subduction zone and the MTZ. Here, we systematically discuss phase transformations of hydrous minerals and the transport processes of water in the subduction system. Furthermore, we analyze possible modes of fluid activity and the problems to explore the applied feasibility of each model. In order to achieve a comprehensive understanding of the mechanisms for thinning and destruction of cratonic lithosphere, we also consider four additional possible dynamic models: extension-induced lithospheric thinning, compression-induced lithospheric thickening and delamination, large-scale mantle convection and thermal erosion, and mantle plume erosion. Compared to the subduction-related models presented here, these four models are primarily controlled by the relatively simple and single process and mechanism (extension, compression, convection, and mantle plume, respectively), which could be the secondary driving mechanisms for the thinning and destruction of lithosphere.     

Subducted slabs beneath the eastern Indonesia-Tonga region: insights from tomography

Tomographic images of mantle structure beneath the region north and northeast of Australia show a number of anomalously fast regions. These are interpreted using a recent plate tectonic reconstruction in terms of current and former subduction systems. Several strong anomalies are related to current subduction. The inferred slab lengths and positions are consistent with Neogene subduction beneath the New Britain and Halmahera arcs, and at the Tonga and the New Hebrides trenches where there has been rapid rollback of subduction hinges since about 10 Ma. There are several deeper flat-lying anomalies which are not related to present subduction and we interpret them as former subduction zones overridden by Australia since 25 Ma. Beneath the Bird’s Head and Arafura Sea is an anomaly interpreted to be due to north-dipping subduction beneath the Philippines-Halmahera arc between 45 and 25 Ma. A very large anomaly extending from the Papuan peninsula to the New Hebrides, and from the Solomon Islands to the east Australian margin, is interpreted to be the remnant of south-dipping subduction beneath the Melanesian arc between 45 and 25 Ma. This interpretation implies that a flat-lying slab can survive for many tens of millions of years at the bottom of the upper mantle. In the lower mantle there is a huge anomaly beneath the Gulf of Carpentaria and east Papua New Guinea. This is located above the position where the tectonic model interprets a change in polarity of subduction from north-dipping to south-dipping between 45 and 25 Ma. We suggest this deep anomaly may be a slab subducted beneath eastern Australian during the Cretaceous, or subducted north of Australia during the Cenozoic before 45 Ma. The tomography also supports the tectonic interpretation which suggests little Neogene subduction beneath western New Guinea since no slab is imaged south of the New Guinea trench. However, one subduction zone in the tectonic model and many others, that associated with the Trobriand trough east of Papua New Guinea and the Miocene Maramuni arc, is not seen in the tomographic images and may require reconsideration of currently accepted tectonic interpretations.     

钙钛矿蠕变对俯冲带震源深度极限的约束

本文利用林伍德石、钙钛矿两种矿物在不同差应力下随温度变化的蠕变曲线,通过约束温度条件和板块俯冲引起的弹性应变率,得到了俯冲带670 km深度可能的应力范围. 结果显示,在俯冲带670 km深度基于林伍德石蠕变得到应力大小可能超过100 MPa,而相变为钙钛矿后仅为0.1~10 MPa. 通过分析认为钙钛矿的Si扩散引起的快速应变率使得670 km更深深度的俯冲带无法支持较大的应力,可能是下地幔地震终止的原因,而不需要考虑亚稳态相变导致反裂隙断层的消失或林伍德石分解后超塑性等影响.     

一组可用于探测亚稳态橄榄石存在情况的震相

基于简化的波速结构,利用二维伪谱法研究了俯冲带不同位置震源激发的地震波的传播特征.发现当俯冲板块中存在6%的低速异常时,直达P波和直达S波之间存在波阵面近平面的易于识别的P-S转换震相,其传播方向不因震源位置偏离低速层的中心而改变.对于低速层的边界存在±2 km的随机起伏、低速层为楔形、周围介质为水平分层模型这三种情况,这组震相仍然清晰可辨.对于150 km长度的橄榄石楔,模拟结果显示仍然能在一定震中距范围内接收到这一震相.因此,可以尝试用这组震相来探测俯冲带亚稳态橄榄石的存在状态.