Crustal structure near Explorer Ridge from a marine deep seismic sounding survey
Crustal structure near Explorer Ridge from a marine deep seismic sounding survey
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海洋深部地震探测显示探险家岭附近的地壳结构
DOI：
10.1029/jb083ib12p05899
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发表时间：
1978
影响因子：
--
通讯作者：
R. Clowes
中科院分区：
文献类型：
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作者：
S. Malecek;R. Clowes
1974年，在东北太平洋的探索者海脊地区记录了两条反向的75公里深地震测深剖面，一条平行于海脊，另一条垂直于海脊。在超过 4 公里的距离处记录的多道地震图在编译为记录部分之前进行了叠加、滤波、静力学和振幅校正。借助合成地震图，利用走时分析和振幅研究对数据进行了解释。对于穿过山脊的反向剖面（74-2 和 74-2R），得出了显着不同的速度-深度曲线。最上面 2.5 公里（底部）类似，速度从大约 2.5 公里/秒快速增加到 5.6 公里/秒。然而，从大约5.6公里/秒增加到6.8公里/秒的深度和形式是不同的。剖面 74-2 显示了一个小的阶梯式增加，随后是一个很大的速度梯度，而 74-2R 则显示了一个大的阶梯式增加，随后是一个较小的梯度。 74-2 所示的更深地壳由到上地幔的单调速度增加组成，但速度梯度不断变化。 74-2R 需要一个深部地壳低速区。有人认为这可能与探险家岭下方的岩浆房有关。对于平行于山脊的两个剖面（74-1 和 IR），还得出了最上地壳中的大速度梯度。我们对旅行时间延迟和偏移的首选解释涉及垂直偏移量约为 5 公里的地壳断层。还给出了低速区的另一种解释。洋壳的海底总厚度在 8 至 10 公里之间变化，断层区域除外，那里的地壳较薄。在上地幔中，在垂直和平行于山脊的方向上测得的反向速度分别为 7.9 和 7.3 km/s；提出各向异性来解释这些不同的速度。根据洋壳岩石学模型和最近对纽芬兰蛇绿岩杂岩的地震速度和岩性结构的测定，讨论了解释的速度-深度模型。在最上层地壳中，大的速度梯度可能是由于玄武岩内大裂缝和孔隙空间的闭合造成的。在下地壳中，我们的结果与涉及不同成分材料之间逐渐过渡的建议是一致的。
In 1974, two reversed, 75-km, deep seismic sounding profiles were recorded in the Explorer Ridge region of the northeast Pacific, one parallel and the other perpendicular to the ridge. Multichannel seismograms recorded at distances beyond 4 km were stacked, filtered, and statics- and amplitude-corrected before compilation as record sections. The data have been interpreted using both travel time analysis and amplitude studies with the aid of synthetic seismograms. For the reversed profiles (74-2 and 74-2R) across the ridge, significantly different velocity-depth curves were derived. The uppermost 2.5 km (subbottom) is similar with a rapid increase in velocity from about 2.5 to 5.6 km/s. However, the depth to and the form of the increase from about 5.6 to 6.8 km/s are different. Profile 74-2 shows a small steplike increase followed by a substantial velocity gradient, while 74-2R has a large steplike increase followed by a lesser gradient. The deeper crust as shown by 74-2 consists of a monotonie velocity increase, but with changing velocity gradient, to the upper mantle. On 74-2R, a deep crustal low-velocity zone was required. It is suggested that this may be associated with a magma chamber beneath Explorer Ridge. For the two profiles (74-1 and IR) parallel to the ridge, large velocity gradients in the uppermost crust also are derived. Our preferred interpretation to explain travel time delays and offsets involves crustal faulting with vertical offsets of approximately 5 km. An alternative interpretation in terms of a low-velocity zone also is given. The total subbottom thickness of the oceanic crust varies between 8 and 10 km, except in the faulted regions, where it is thin. In the upper mantle, reversed velocities of 7.9 and 7.3 km/s are determined in directions perpendicular and parallel to the ridge; anisotropy is proposed to explain these different velocities. The interpreted velocity-depth models are discussed in terms of petrologic models of the oceanic crust and recent determinations of the seismic velocity and lithologie structure of a New-foundland ophiolite complex. In the uppermost crust, the large velocity gradients probably result from the closing of large cracks and pore spaces within the basalt. In the lower crust, our results are consistent with proposals involving gradual transitions between material of differing composition.