Exploring the Bounds and Limits of GIS
A short blog about what I am doing and learning in relation to Geographic Information Systems. I explore different techniques as well as different GIS platforms, and report my experiences, successes, and failures.
Monday, November 29, 2021
Wednesday, May 2, 2018
Earthquake focal depth vs. magnitude: Are they correlated?
Lately I began to wonder: does the depth of focus of an earthquake correlate to its magnitude? I asked some colleagues. They said no. But I wanted to find out for myself. So I did.
I decided to go back to the NCEDC to get some data. I did a search and set the lower limit for magnitude to 3, no limits for depth or long/lat. I limited it to nothing before 1970 because some of the data such as depth or magnitude were missing before then. I asked to to return it to me in "csv format" (which still comes as a webpage). Then I set the line limit to 1,000,000. I wanted all the data points I could get. And I got them. All 583,000 or so points. I initially asked for 50,000, and got those too, but they weren't enough. Each point comes with long/lat, magnitude, depth, data, and more that I am not concerned with. Turns out the 583,000 entry .csv is ~46 mb as a .csv or .txt. If I convert it to points in ArcGIS the .dbf (database file) is 500+ mb alone. Damn.
To find the answer to my question I did two things. First, I played with some Python to let it to the stats on the magnitude and depth to find the correlation. Python suggests that no, they aren't correlated. You can see the iPython Jupyter Notebook I created for it here. Gotta love Python.
For the bit in brackets, the important number are the middle two. They are the calculated correlation values between depth and magnitude. Python's Numpy library displays it that way. I would write a function to do the same thing and output in a nice format, but why re-invent the wheel?
Secondly, while number are all fine and good, it might be nice to see this a little more visually. This is where the interpolation comes in. As I had over 500,000 points, covering the whole globe, we can get a good picture of both the depth and magnitude of earthquake across the whole planet. I went with IDW interpolation as Kriging 500,000+ points makes Arc lose its mind. Running the Kriging interpolation never finished.
I decided to go back to the NCEDC to get some data. I did a search and set the lower limit for magnitude to 3, no limits for depth or long/lat. I limited it to nothing before 1970 because some of the data such as depth or magnitude were missing before then. I asked to to return it to me in "csv format" (which still comes as a webpage). Then I set the line limit to 1,000,000. I wanted all the data points I could get. And I got them. All 583,000 or so points. I initially asked for 50,000, and got those too, but they weren't enough. Each point comes with long/lat, magnitude, depth, data, and more that I am not concerned with. Turns out the 583,000 entry .csv is ~46 mb as a .csv or .txt. If I convert it to points in ArcGIS the .dbf (database file) is 500+ mb alone. Damn.
To find the answer to my question I did two things. First, I played with some Python to let it to the stats on the magnitude and depth to find the correlation. Python suggests that no, they aren't correlated. You can see the iPython Jupyter Notebook I created for it here. Gotta love Python.
Earthquakes 1970-1978: Depth standard dev: 1.708 Depth variance: 2.917 Magnitude standard dev: 2.882 Magnitude variance: 8.306 depth vs. magnitude correlation: [[ 1. 0.00593409] [ 0.00593409 1. ]] The two middle values are the correlation for depth amd magnitude to one another. Earthquakes 1970-2018: Depth standard dev: 1.708 Depth variance: 2.918 Magnitude standard dev: 2.872 Magnitude variance: 8.248 depth vs. magnitude correlation: [[ 1. 0.00236923] [ 0.00236923 1. ]] The two middle values are the correlation for depth amd magnitude to one another.
For the bit in brackets, the important number are the middle two. They are the calculated correlation values between depth and magnitude. Python's Numpy library displays it that way. I would write a function to do the same thing and output in a nice format, but why re-invent the wheel?
Secondly, while number are all fine and good, it might be nice to see this a little more visually. This is where the interpolation comes in. As I had over 500,000 points, covering the whole globe, we can get a good picture of both the depth and magnitude of earthquake across the whole planet. I went with IDW interpolation as Kriging 500,000+ points makes Arc lose its mind. Running the Kriging interpolation never finished.
I am forced to conclude that there appears to be little mathematical evidence for a correlation between earthquake magnitude and depth as well as the more qualitative representation on a map. The map, however, shows an interesting pattern that the smaller earthquakes are concentrated in Europe, North America, and Australia. I don't fully know why as of yet.
Saturday, April 28, 2018
HAZUS, Earthquakes, and Tsunamis
Predicting
when an earthquake will occur can be very difficult, likewise with tsunamis.
While we may not be able to predict them, we can at least create models to aid
in preparedness in the event that one does occur. FEMA's HAZUS software allows
us to do just that with the power of ArcGIS® 10.5.1. In this project I decided
to revisit my two study areas in Anchorage and Los Angeles from my second
project (Figure 1). I went with HAZUS since modeling tsunamis
requires extensive maths and the modeling software TSUNAMI-N2 by Goto et al.,
1997 is written in FORTRAN. HAZUS is quite large, power, and complex.
To model the tsunamis, I gave HAZUS default parameters laid
out in the HAZUS Tsunami User Manual. I set the maximum runup to 20m for
both study areas. I was expecting Anchorage to get completely inundated and
coastal California to be protected by the coastal cliffs. My predictions were
incorrect (Figures 2 and 3). Tables 1 & 2 compared damages and casualties.
Table 1 – Tsunami Damage to Buildings by
Count by General Occupancy
Agriculture
|
Commercial
|
Education
|
Government
|
|
Anchorage
|
32
|
978
|
72
|
12
|
Los
Angeles
|
57
|
110
|
3
|
1
|
Industrial
|
Religion/Non-Profit
|
Residential
|
Total
|
|
Anchorage
|
164
|
26
|
3488
|
1094
|
Los
Angeles
|
657
|
9
|
44780
|
171
|
Table 2 - Tsunami Casualties by Community Preparedness
Community
Preparedness
|
||||||
Day
|
Good
|
Fair
|
||||
Fatalities
|
Injuries
|
Total
Casualties
|
Fatalities
|
Injuries
|
Total
Casualties
|
|
Anchorage
|
8602
|
1055
|
9657
|
10533
|
665
|
11198
|
Los Angeles
|
1005899
|
71948
|
1077847
|
2412297
|
70164
|
2482461
|
Day
|
Poor
|
|||||
Fatalities
|
Injuries
|
Total
Casualties
|
||||
Anchorage
|
11137
|
397
|
11534
|
|||
Los Angeles
|
5465410
|
62210
|
5527620
|
|||
Night
|
Good
|
Fair
|
||||
Fatalities
|
Injuries
|
Total
Casualties
|
Fatalities
|
Injuries
|
Total
Casualties
|
|
Anchorage
|
7355
|
1362
|
8717
|
9981
|
973
|
10954
|
Los Angeles
|
1001019
|
71720
|
1072739
|
2357493
|
68267
|
2425760
|
Night
|
Poor
|
|||||
Fatalities
|
Injuries
|
Total
Casualties
|
||||
Anchorage
|
10937
|
577
|
11514
|
|||
Los Angeles
|
5304326
|
60138
|
5364464
|
Figure 2 - Tsunami runup in the Anchorage area. Surprisingly, most of Anchorage is untouched. I hadn't realized that most of Anchorage actually sits at about 100' of elevation. |
Similar to the tsunami model, I followed a basic earthquake
model, though with some modifications. For Anchorage I set the earthquake model
to Alaska or Puerto Rico / VI – Reverse
as I assumed a reverse fault would rupture given Alaska is in an active
subduction zone. For Los Angeles I ran two models, one strike-slip for the San
Andreas fault and one reverse for the Catalina fault. Table 3 compares
casualties Table 4 shows damages to buildings.
Table 3 - Combined Earthquake Economic
Loss and Casualties in Magnitude 7 Event
Economic
Loss - Buildings ($)
|
Economic
Loss - Transportation
($)
|
|
Anchorage
|
2,909,951,000
|
182,302,000
|
Los
Angeles (strike-slip)
|
7,933,660,000
|
69,821,000
|
Los
Angeles (reverse)
|
4,340,831,000
|
73,512,000
|
Economic
Loss - Utilities ($)
|
Shelter
Req's (# people)
|
|
Anchorage
|
0
|
1647
|
Los
Angeles (strike-slip)
|
16,480,000
|
2234
|
Los
Angeles (reverse)
|
6,150,000
|
791
|
Anchorage
|
Casualties
- 2am
|
Casualties
- 2pm
|
Los
Angeles (strike-slip)
|
454
|
1250
|
Los
Angeles (reverse)
|
1231
|
362
|
472
|
902
|
|
Anchorage
|
Casualties
- 5pm
|
|
Los
Angeles (strike-slip)
|
867
|
|
Los
Angeles (reverse)
|
1959
|
|
627
|
Table 4 - Earthquake Damage to Buildings
by Count by General Occupancy
Location
|
Agriculture
|
Commercial
|
Education
|
Government
|
Industrial
|
Anchorage
|
5033
|
2916
|
110
|
178
|
762
|
Los
Angeles (strike-slip)
|
425
|
16916
|
511
|
275
|
4770
|
Los
Angeles (reverse)
|
269
|
13491
|
360
|
232
|
3855
|
Location
|
Other
Residential
|
Religion
|
Single
Family
|
Total
|
|
Anchorage
|
8127
|
258
|
91922
|
8999
|
|
Los
Angeles (strike-slip)
|
29377
|
1242
|
177547
|
22897
|
|
Los
Angeles (reverse)
|
21409
|
1002
|
96055
|
18207
|
Figure 4 - Ground motion in Anchorage at 1 second (top) and 0.3 seconds (bottom). |
Figure 5 - Ground motion due to movement along the San Andreas fault at 1 second (top) and 0.3 seconds (bottom). |
Figure 6 - Ground motion due to movement of a reverse fault offshore at 1 second (top) and 0.3 seconds (bottom). |
In conclusion, HAZUS can provide some useful data for
predicting what could happen and where. The model predicts that casualties due
to an earthquake would be much lower than those from a tsunami, however
building damages from an earthquake would be much more devastating. A link to
the report can be found here.
Subscribe to:
Posts (Atom)