Final answer:
An ArcGIS user analyzing an earthquake dataset for magnitude and duration is using a scatter plot, as it helps to determine the relationship between the two continuous variables.
Step-by-step explanation:
The type of graph an ArcGIS user employs when analyzing an earthquake dataset with magnitude on the x-axis and duration on the y-axis is a scatter plot. This kind of graph is used to display and determine the relationship between two quantitative variables. Each point on the scatter plot represents an individual data point with its x-value denoting the magnitude and the y-value representing the duration of an earthquake incident. By observing the pattern of the dots, researchers can determine if there is any correlation between the two variables, such as a positive correlation, negative correlation, or no correlation at all.
A scatter plot is distinct from other types of graphs such as a histogram which is used for showing the distribution of a single quantitative variable or a bar graph which is typically employed to compare different groups. Neither the box plot which is useful for showing the distribution of a dataset and its quartiles nor the histogram would be appropriate for analyzing the relationship between these two continuous variables. Thus, the correct option for this type of analysis is a scatter plot.