The movement history of boulders is crucial for the reconstruction of paleo-tsunamis. We report findings from viscous remanent magnetization studies of the boulders on Tongatapu Island, aiming to reconstruct their reworkings. Two boulders exhibited viscous remanence, whereas two larger boulders lacked viscous components but exhibited stable remanence. Both the viscous and stable components deviated from the geomagnetic field direction. These observations indicate that: (a) the boulders with a viscous component were reworked before the latest event, which could have reworked all boulders, and (b) the magnitude of the latest event was larger than that of an earlier event. The reworked timing indicated that the event occurred between 3,000 years ago and the fifteenth century. The difference in the wave height required to move boulders on the eastern and western coasts suggests that the source of the earlier tsunami was likely an eruption due to volcanoes along the Tonga Ridge.

中文翻译：

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汤加王国再加工巨石的粘性剩余磁化的古代海啸记录


巨石的运动历史对于古海啸的重建至关重要。我们报告了汤加塔布岛上巨石的粘性剩余磁化研究结果，旨在重建它们的再加工。两块巨石表现出粘性剩磁，而两块较大的巨石缺乏粘性成分，但表现出稳定的剩磁。粘性和稳定组分都偏离了地磁场方向。这些观察结果表明：（a） 具有粘性成分的巨石在最近一次事件之前被重新设计，这可能已经重新加工了所有巨石，以及 （b） 最近一次事件的震级大于早期事件的震级。重新设计的时间表明，该事件发生在 3,000 年前至 15 世纪之间。在东西海岸移动巨石所需的波高差异表明，早期海啸的来源可能是汤加海脊沿线火山喷发。