FAQ: Interactive Maps

This weblog is designed as a research tool for people interested in current and past earthquake activity. The west coast of the United States is our main focus. However, we do special reports for significant earthquakes around the world.

OUR MAPS- We use Google Earth for our primary maps. Our earthquake maps are divided into three west coast regions:

• Southern California (31.5 37.0, -129.5 -114.0)
• Northern California(36.5 42.4, -129.5 -116.9)
• Oregon & Washington (41.9 49.2, -129.5 -115.7)

Watch for maps and lists in our special reports as well. Our special reports feature maps of significant earthquake events from all over the country and other parts of the world.

Earthquakes are plotted on these maps using a custom program created specifically for this project.

DATA
Earthquake data comes from various sources. The ANSS Composite Earthquake Catalog, is used for all regions. Southern California also uses data from the Southern California Earthquake Data Center. Northern California also uses data from the Northern California Earthquake Data Center.

The ANSS catalog uses composite data from several sources. To create a more complete report, we supplement this data with data from SCEDC and NCEDC. It's common to have the same earthquake listed twice with differing details. Our software eliminates these duplicates and uses the listing with the largest magnitude.

INTERACTIVITY
Our maps are interactive. You can click on larger quakes (usually 5.0+) to see a closer map of that specific area. These special maps are produced only for larger quakes that occur over land within the boundaries of the United States.

COLORS & SIZES
Earthquakes displayed on the maps are seen in various sizes and colors. The size of the quake icon refers to the magnitude of the earthquake. The color of the icon refers to the relative age of the earthquake.

The colors of the quakes is a question I am often asked. What do they mean? The colors of a quake represent the relative age of the quake. I know what you are thinking now, "so, what does THAT mean"? It's not a simple question to answer but I will try.

The color scheme always follows a yellow to red gradient. The very first earthquake to occur (within that dataset) will ALWAYS be yellow and the last quake to occur will ALWAYS be red. All other quakes will be colored based on where it falls on the timeline between the first and last quakes of the dataset.

The easiest way to explain this is to demonstrate a very small dataset. Lets say we are listing three quakes. The first quake occurred on Monday and is colored yellow. The last quake occurred on Wednesday and is colored red. The second quake occurred on Tuesday. This quake would be colored orange because orange is half red and half yellow. Now if the last quake occurred on Friday instead of Wednesday. The Tuesday quake would be more yellow than red because it is relatively older based on the data set.

A map that feauteres data for a full year (Jan thru Dec) will show quakes occuring early in the year as yellow, and red for quakes occuring later in the year.

Another way to look at the colors is to always remember that quakes that are of similar colors occurred around the same time. All quakes that occur on the same day will always be the same color (regardless of the dataset).

Creating a dynamic color scheme like this allows us to create some very unique and informative maps. Look at this example for instance. This map used a dataset that included only the 1971 San Fernando quake and aftershocks, and the 1994 Northridge quake and its aftershocks. It's now easy to distinguish which quake belongs to which event. This would be impossible if they were all the same color.

LISTS
Our maps will have an accompanying quake list which shows the Magnitude, Date, Time, location, and Depth of the quake.

All times are listed as UTC time.

The locations are determined using our own special software.

ARCHIVES
We are slowly working our way back in time to create maps and lists for previous years. We will go back as far as accurate records will allow.