Earthquake induced landslide hazards in Anchorage, Alaska and Los Angeles, California - A comparison

For this project I decided to compare the risk of earthquake induced landslides around Anchorage, Alaska and western Los Angeles, California as both areas are affected by active seismicity. 
To do my comparison I first acquired data on cataloged earthquakes in Alaska and California. The following were done on data for both study areas:

- Drew buffers around earthquakes where the radius = 27.306(x)2 – 238.96(x) + 510.08, based on Keefer, 1984 and derived using Excel. I explain it here.
- Slopes were derived from 10 DEMs.
- Ran Con on the rasters of the slopes for all slopes above 30° and all slopes above 45°, then converted them to polygons.
- Land cover rasters were converted to polygons and all but the urban sections were removed. 
- All slopes of 30°+ were selected within 50m of urban areas, buffered and dissolved. Same for 45° for 50m and 150m.
I chose 30° and 45° as they are a bit below and above, respectively, the angle of repose for most geological materials. 

Figure 1 - Earthquakes in Alaska with buffers drawn around them. All earthquakes were magnitude 6 and above.

Figure 2 - Earthquakes in California above magnitude 5.06.

Significantly more areas with steep slopes near or intersecting urban areas were found in California. The Anchorage DEM covered approx. 5824 km2 with roughly 37 km2 at risk (Figure 3). The California DEM covered approx. 10192 km2 with about 1262 km2 at risk (Figure 4). 

Figure 3 - Alaska, Anchorage Area

Figure 4 - California, Los Angeles Area

To ‘ground truth’ how well my model worked I used Google Earth’s Street View in a few selected places. Street View seems to have corroborated my GIS findings as seen in figures 6 and 8.

Figure 5 - One of the few areas with steep slopes in the Anchorage Area. 

Figure 6 - Google Earth Street View Image of the the area in the above map. Going south along Hatcher Pass Road, north of Fishhook, Matanuska-Susitna County, Alaska, . It is evident that the DOT is aware of this area as a hazard as the outcrop has been cut back from the road and a fence has been put in to keep loose boulders from making it to the road. The rocks here are sedimentary.

Figure 7 - A section of the Pacific Coast Highway near Big Rock, Los Angeles County, California. Significant areas at risk can be seen here, the red being areas with slopes of 45° or more within 50m of urban areas (roads included).  

Figure 8 - The same stretch of the Pacific Coast Highway shows in Figure 6. Note how close the slope comes to the road, and how steep it is. 

This model is far from perfect as it doesn’t consider lithology, soil conditions, engineered slopes, the role of vegetation, or precipitation, which all factor into landslide occurrence.

The full report can be viewed here.