California Earthquakes: High Impact Observations and Risk Zones

Earthquakes small and large are an integral part of California’s geographic reality. As the USA’s most populous state, the threat of earthquakes and other natural disasters imposes very real risks and challenges to a significant number of residents. Even with increasingly sensitive and advanced technology to measure seismic activity, these events are detectable but not predictable. This GIS project uses mapping tools and datasets to identify populations directly along fault lines and locations of epicenters for past earthquakes of magnitude 5+. Using QGIS, shapefile layers, and data tables, we may create a visualization to display historical and current areas of high risk to these natural disasters.

The Data

California Census Tracts for population counts in California, shapefile for State of California, shapefile for California fault lines, historic earthquake data retrieved from US Geological Survey (includes long-lat coordinates for plotting).

Data Sources:

ISC-GEM Global Instrumental Earthquake catalog, V 6.0 released 2019-03-07 (http://www.isc.ac.uk/iscgem/download.php)

Fault Activity Map of California, 2010-12-31 (https://maps.conservation.ca.gov/cgs/#datalist)

California TigerLine Shape files for Census Tracts in California (https://www.census.gov)

California Census Tract Population Data (https://factfinder.census.gov)

2017 ACS 5Yr Est Data + People: Basic Count Population + All Census Tracts within California

2017 ACS 5Yr Est Data + S1901: Income & Earnings (Households) + All Census Tracts within California

Understanding Impactful Measures

Historic earthquakes were scored based on a composite figure incorporating Moment Magnitude and Depth.

Moment Magnitude (mw)

4.0-5.0: Destructive

5.0-6.0: More Destructive

6.0 and Above : Most Destructive

Depth (uncorrelated to magnitude)

0-70km Shallow (colder, more brittle)- most surface damage

70-300km Medium

300-700km Deep (warmer, less brittle) - least surface damage

First the historic earthquake points were applied to a California base map.

The shapefile of fault lines was then applied to the map.

The historic earthquakes were scored based on Moment Magnitude (mw) and Depth of event.

Los Angeles base map. Adding labels with years creates a layer of historic quake occurrences overlaid on the geographic data. Darker points represent more destructive earthquakes.

Calculating Population AT Risk

GIS has tools to calculate square area of the tracts and add customized buffer zones around the fault lines. To create a calculation of “at risk” population numbers, divide the buffer zone area by the whole tract area to get the percentage of fault area to total area in the tract. Then multiply that percentage to the total population of the tract.

Los Angeles: In the final visualization for the project, the fault lines are shaded according to population density. Darker lines show the areas of faults that travel through more densely populated areas. The lines in red indicate the most populous … — Los Angeles: In the final visualization for the project, the fault lines are shaded according to population density. Darker lines show the areas of faults that travel through more densely populated areas. The lines in red indicate the most populous segments at risk: 1200-4400 people per tract segment.

San Francisco: In the final visualization for the project, the fault lines are shaded according to population density. Darker lines show the areas of faults that travel through more densely populated areas. The lines in red indicate the most populou… — San Francisco: In the final visualization for the project, the fault lines are shaded according to population density. Darker lines show the areas of faults that travel through more densely populated areas. The lines in red indicate the most populous segments at risk: 1200-4400 people per tract segment.