Key Learning: After shocks vs Magnitude correlation. The two graph insets were surprising to me. They clearly show that while the number of aftershocks per day decreases over time, the magnitude does not necessarily weaken.
Background: By summarizing the data in a table, one can derive various summary statistics—including the count, average, minimum, and maximum values—and get exactly the information needed. Information gleaned from data sources such as tables and graphs complement a map because they convey information that would otherwise take more time to summarize and understand. Using this map as an example, a user can quickly compare features to see which have more or less of a particular attribute.
Summary of Steps to "Get There"
1) Open Northridge3.mxd in ArcGIS
2) Open the attribute table for Earthquakes layer and summarize the DaysAfter column by maximum magnitude.
3) Save the output as Aftershocks.dbf, then add to map
4) Opened new table and under options clicked Create Graph
5) Create a graph setting the Value to Count_DaysAfter and the X field to DaysAfter and then created a graph with the Value as Magnitude and X field still Days after.
6) Rearranged figure to fit both the map and two graphs and exported
Review questions:
1. How can an earthquake scenario map be used to identify population and infrastructure that would be affected by the hypothetical event?
"By simply observing the point features, you can see that there are concentrations of building damage in certain places. A density analysis of the building damage will help to reveal additional patterns of concentrations that are not apparent when looking at the features alone. The Spatial Analyst Density function enables you to measure the number of features in a study area based on some standard unit of area. In this step, you will measure the number of damaged buildings per square kilometer" Earthquake Part II lab, page 4.
"By simply observing the point features, you can see that there are concentrations of building damage in certain places. A density analysis of the building damage will help to reveal additional patterns of concentrations that are not apparent when looking at the features alone. The Spatial Analyst Density function enables you to measure the number of features in a study area based on some standard unit of area. In this step, you will measure the number of damaged buildings per square kilometer" Earthquake Part II lab, page 4.
2. What GIS function would allow you to create a damage pattern map from a GIS layer of damaged buildings?
"GIS, digital photogrammetry, and digital positioning data produce 3D earthquake fault maps, [therefore] fault rupture maps created with GIS software show the rupture pattern of the … earthquake[s] and how branching faults come together."Geologic Fault-Finding with GIS http://www.esri.com/news/arcnews/fall08articles/usgs.html .
3. How can GIS help you visualize a fault plane after an earthquake.
There are several ways to visualize a fault plane. A very comprehensive paper I found was "Various 3D angle views of the fault help scientists better understand earthquakes” Geologic Fault-Finding with GIS. http://www.esri.com/news/arcnews/fall08articles/usgs.html.
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