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4.0GPa压力下纯橄岩弹性纵波速度和衰减的实验研究

DOI: 10.11858/gywlxb.2005.04.002, PP. 293-298

Keywords: 高压,纵波速度,衰减,品质因子

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Abstract:

应用超声波透射法和超声波频谱振幅比法、在4.0GPa压力条件下、测量了弹性纵波通过纯橄岩的波速(vP)和品质因子值(QP,用于表征衰减)随压力的变化,并分析了纯橄岩内部结构的变化对波速和衰减的影响。在实验压力范围内(≤4.0GPa),随压力升高,纯橄岩的纵波速度逐渐增大:从7.6km/s(0.4GPa)逐渐增大至8.5km/s(4.0GPa),升高了11.8%,低压时的增大幅度大于高压时的增大幅度。纯橄岩的品质因子值呈两段式线性变化:从低压区间到高压区间品质因子值的增大幅度明显变小(0.4~2.4GPa压力范围内QP增大了358.5%,2.4~4.0GPa压力范围内QP仅升高了7.6%)。纯橄岩的品质因子从54(0.4GPa)升高至266.4(4.0GPa),增大幅度达393.3%。在相对低压(0.4~2.4GPa)条件下,纵波通过纯橄岩的速度增大、衰减降低主要是由于样品内的孔隙和微裂纹大量闭合,岩石密度增大,纵波在通过样品内孔隙和裂缝时损失的机械能降低,因此纵波通过纯橄岩的能量增大(即衰减降低),波速升高;当围压较高(2.4~4.0GPa)时,纯橄岩内大部分裂纹已经闭合,而且矿物颗粒边界接触紧密。岩石内部的裂纹和颗粒之间由于摩擦滑动而损失的能量也变少,所以在高压时纯橄岩的波速和衰减的变化幅度变缓,但波速仍呈线性增大,而品质因子值(衰减)随压力升高几乎趋于不变。

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