Basal conditions of Malaspina Glacier

In this active seismic experiment we will collect AVO data at two glacier sites. One is located over a glacier bed high and the other one over a depression. The goals is to use Amplitude vs Offset methods to determine the nature of the subglacial material. A line of 24 geophones will be buried in snow to protect them from wind noise and the line will be accurately surveyed with GPS. A set of 100 shot holes will be drilled into the underlying ice to obtain a large range of offsets, so that amplitudes can be compared over large offset angles. If possible, the data will also be used to find the thickness of a subglacial till layer. The seismic experiment is part of a large geophysical and remote sensing observational program with the goal to provide input data for an ice flow model that will explore possible future scenarios for this large glacier that is very vulnerable to future climate change. In a second experiment we will do attempt to measure the extent of buried ice in the glacier foreland. For this experiment we propose to use 4.5 Hz geophones and we will use a hammer for the active source. This is part of the same NSF funded work.

本次主动源地震实验将在两处冰川观测点位采集振幅随偏移距变化（Amplitude Versus Offset，AVO）数据：一处位于高海拔冰川床之上，另一处则坐落于冰蚀洼地内。本实验的目标为利用AVO方法，明确冰下物质的组成性质。我们将布设一条包含24个检波器（geophone）的测线并埋入积雪中，以规避风噪声干扰；同时将通过GPS对该测线开展精准测绘。此外，我们将在下方冰层中钻取100个炮孔，以获取大范围的偏移距覆盖范围，从而能够在大偏移距角度下开展振幅对比分析。若条件允许，本次采集的数据还将用于估算冰下冰碛层的厚度。本次地震实验隶属于一项大型地球物理与遥感综合观测计划，该计划旨在为冰流模型提供输入数据，借此模拟这座极易受未来气候变化影响的大型冰川的未来演化情景。在第二项实验中，我们将尝试测定冰川前缘区域的埋藏冰分布范围。针对本次实验，我们计划使用4.5Hz的检波器，并以铁锤作为主动震源。本项实验同样隶属于美国国家科学基金会（National Science Foundation，NSF）资助的研究项目。