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距离震中与距离的焦点

我不是一个“初露头角的地震。”I am a chemistry/physics teacher teaching an Earth science class (low academic level) in a small-town high school. (My college coursework in earth sciences = 0) I understand the concept of triangulation to determine an earthquake's origin, and I realize there are some subtleties in wave analysis such as pP and sP waves. What I don't understand is how the triangulation determines the epicenter instead of the focus. Wouldn't the S-P lag times for 3 stations give an intersection point at the focus since that is the actual point of origin for the waves?

回答

在地图上画圆的方法找到他们的交集只解决了一个未知数。当站远离震源地震或虽浅,焦点和中心之间的距离之间的差别将被忽略。因为许多地震是浅,三圈经常做相交于一点。当他们不这样做,一个可能的解释是,因为地震相对深度(与震中的距离。)如果你想尝试确定震中和地震的深度,那么您需要收集更多的观察(站)和用数学来解决系统至少有两个未知数。您可以使用线性代数。注意站到达时间接近地震将受到关注的深度的影响比站远,所以你会想要包括车站靠近地震。中学物理学生可能有足够的数学使用[牛顿迭代方法][1]的方法来估计深度。他们可能会使用的初始估计的“震中”第一个方法,试图解决的约束方程来估计一个深度。在实践中,地震学家收集大量的数据,必须考虑许多未知数,如距离焦点,而且地震速度的变化通过不同类型的岩石。 If you try the three-station and map approach in your Earth Science classroom, the students may notice that all three circles do not go though a single point typically, but come more or less close to doing so. Perhaps this is a good opportunity to discuss the differences between a model and actual earthquakes and Earth. It might even be possible to discuss how a better model can improve the agreement with observations. It looks like this USGS page : [Determining the Depth of an Earthquake][2] has a somewhat different answer, which may describe how deep earthquakes were 'discovered' historically :) [This presentation][3] at the Berkeley Seismographic Station shows a geometric construction and formula for determining earthquake depth. [1]: http://mathworld.wolfram.com/NewtonsMethod.html [2]: http://earthquake.usgs.gov/learn/topics/seismology/determining_depth.php [3]: http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0CCYQFjAB&url=http%3A%2F%2Fseismo.berkeley.edu%2F~rallen%2Fteaching%2FF04_GEO302_PhysChemEarth%2FLectures%2FL03_EarthquakeSource.pdf&ei=RSbiVIK_FIn0oATKvICICQ&usg=AFQjCNFrvjhZylNXO0hzXuQP2qocuHialw

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