The UCERF 3 Earthquake Catalog
K. R. Felzer
The UCERF3 catalog is given in a 15 column format as follows:
1) Year
2) Month
3) Day
4) Hour
5) Minute
6) Second
7) Latitude
8) Longitude
9) Depth
10) Magnitude
11) Magnitude type (given as ‘0’ for pre-instrumental magnitudes)
12) Magnitude source
13) Magnitude uncertainty (standard error; given as ‘0’ if unknown)
14) Magnitude rounding (for example, given as 0.1 if magnitudes are written as
4.1, 4.0; given as 0.5 if magnitudes written as 5.0, 5.5, etc.)
15) Earthquake ID (given as ‘99’ if not assigned by network or source catalog)
The magnitude type and magnitude source are given as numerical codes so that the
catalog can easily be read into data processing programs. The codes are as follows:
Table 1
Code
1
2
3
4
5
6
7
8
9
Magnitude type
ML
Mb
Mc
Md
Mh
MS
MW
MX
Unk
Code
1
Magnitude source
AK (Alaska Regional Network)
Table 2
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
BK (Berkeley)
BRK (Berkeley)
BSE (Boise State University)
CI (Southern Cal. Seismic Network)
DOE (DOE explosion)
ECX (CICESE, Mexico)
EXP (non-DOE explosion)
GLD (USGS Golden)
MNL (USGS Menlo Park)
NC (Northern Cal. Seismic Network)
NEIC
NN (Nevada Seismic Network)
PAS (CalTech, Pasadena)
REN (University of Nevada, Reno)
SEA (University of Washington, Seattle)
UNM (UNAM, Mexico City)
USG (USGS not covered elsewhere)
UU (Utah seismic network)
UW (Pacific Northwest Seismic Network)
Global CMT catalog
Tsai and Aki, (1969)
The source catalog for an earthquake’s location is not given in the catalog, however
the source of an earthquake’s magnitude and location are the same except for two
exceptions: 1) If an earthquake is assigned a magnitude from the global CMT
catalog its location is from the local network, which usually has a better location and
2) Events from 1942-1984 along the San Andreas system in Northern California are
assigned magnitudes from the Berkeley catalog but locations from the NCSN
(Northern California Seismic Network) catalog based on the assessment of Bill
Ellsworth (personal communication) that these locations have higher accuracy. The
area with the Berkeley magnitudes but NCSN locations is bounded by the following
lat/long: [35.17,-121.06; 36.67,-122.67; 38.75,-123.91; 38.81,-122.05; 36.45, 118.99; 35.06,-121.06]. This issue is discussed further below along with more
detailed documentation of the catalog.
1769 – 1850
Earthquakes during this time period are very poorly constrained and the catalog is
very incomplete. It is recommended that these earthquakes not be used for seismic
rate calculations or other hazard analysis.
1850 – 1932
This portion of the catalog is the same as the catalog published for UCERF2 (Felzer
and Cao, 2008) and is based on the California Geological Survey (CGS) catalog
compiled by Mark Petersen and the University of Nevada historical catalog. Many of
the events during this time period are historical, with magnitudes estimated from
felt accounts. Many of the solutions originate from the work of Toppozada and coworkers with some contributions from other authors who investigated historical
earthquakes; a full reference list is given in Felzer and Cao (2008). Solutions for
many of the events solved for by Toppozada were also derived in papers by Bakun
and co-authors. Earthquakes for which an alternate solution by Bakun exists and
the appropriate references are given in Felzer and Cao (2008). Felzer and Cao
(2008) found that using either the Toppozada or Bakun solutions for post-1850
earthquakes had nominal impact on final seismicity rates. One important
difference, however, is that the method of Bakun allows for the assignment of
magnitude uncertainty to historical earthquakes whereas Toppozada’s method does
not. Thus the magnitude uncertainty derived by Bakun was used for earthquakes
for which the magnitudes solved for by both authors was within the error found by
Bakun. When this criteria was not satisfied, or when an earthquake had not been
investigated by Bakun, an uncertainty of 0.333 was assigned. Different
uncertainties were assigned to a few earthquakes on a case by case basis, where
solutions by Toppazada and Bakun were close but not with the error set by Bakun.
A full discussion of the magnitude uncertainty assignment for historical earthquakes
is given in Felzer and Cao (2008).
1932-2011
The full instrumental catalog starts for southern California in 1932. Routine
standardized magnitude calculation started in northern California in 1942, but some
instrumental solutions exist for this region back to the early 1900s. The southern
California seismic network underwent an upgrade in 1984, and catalog
completeness improved significantly. Therefore we catalog only M≥4 earthquakes
prior to 1984, but include M≥2.5 earthquakes afterwards.
Our base catalog for this time period is the composite catalog of the ANSS (Advanced
National Seismic System), which includes contributions from a number of different
networks. The ANSS catalog was downloaded on 10/11/2011 and data through
9/30/2011 was included in the download. Note that earthquake catalog solutions
are re-analyzed so solutions for any of the earthquakes that we downloaded may
change over time. Nuclear test explosions and other blasts were removed from the
catalog.
Southern California solutions from the ANSS catalog were checked against a
contemporary download of the Southern California Seismic Network Catalog
(SCSN). The solutions were found to be the same, indicating that updates being
made in the SCSN catalog were also being made in the ANSS listing. Magnitude
uncertainties however, were not provided in the ANSS or SCSN listing. The station
amplitudes and station corrections that were used to calculate the magnitudes were
provided from the SCSN data base courtesy of Ellen Yu; these were used to calculate
magnitude uncertainties. When station amplitudes were not available for an event
magnitude uncertainty was estimated from the uncertainties of other earthquakes
of similar location, time, and magnitude using the following algorithm:
1) Select all earthquakes within ±0.5 magnitude units.
2) For all of the selected earthquakes measure the metric D between these
earthquakes and the earthquake that is missing an error where D =
Difference in latitude + difference in longitude + difference in time.
3) Take the mean uncertainty of the 10 earthquakes with the smallest value of
D.
4) Round the uncertainty to the nearest 0.01 place and then add 0.00333 to
indicate that the uncertainty is an estimated value.
The Northern California Seismic Network (NCSN) catalog was downloaded on
10/27/2011 and checked against the ANSS download. Some differences were
found. Where the earthquake in question was within the NCSN region and ANSS
reported the earthquakes as originating from the NCSN catalog I presumed that the
NCSN solution was the more recent one and replaced the ANSS listing in the catalog.
The NCSN catalog includes magnitude uncertainties for many earthquakes. When
the uncertainty was not listed it was approximated from surrounding earthquakes
as detailed above.
Bill Ellsworth (personal communication) reported errors in the pre-1984 Northern
California magnitudes listed in the ANSS catalog due to errors in a recent conversion
of the magnitudes to Md. Therefore on his recommendation these magnitudes were
replaced with original ML magnitudes from the Berkeley catalog, although
ANSS/NCSN locations were retained along the San Andreas system as specified
above, also per his recommendation. In the absence of more event-specific
information all Berkeley magnitudes were assigned the catalog average magnitude
uncertainty of 0.14 on the advice of Robert Uhrhammer (personal communication).
Earthquakes were also contributed over this time period from the Nevada Seismic
Network. Nevada events prior to 1990 were assigned a magnitude uncertainty of
0.4 and events after 1990 an uncertainty of 0.27 based on the recommendations of
John Anderson and Glenn Biasi. We are currently waiting for magnitude uncertainty
estimates from the University of Washington network; in the meantime these
uncertainties are listed as zero.
Moment magnitude (MW) solutions from the global CMT catalog are available for
most M>5.4 earthquakes in California after 1977. ANSS magnitudes were replaced
with the MW solutions whenever possible. A standard uncertainty of 0.09 was
assigned to all global CMT catalog earthquakes based on the findings of Kagan et al.
(2006).
References
Felzer, K. R. and Cao Tianqing, WGCEP Historical California earthquake catalog,
Appendix H in The Uniform California Earthquake Rupture Forecast, version 2
(UCERF 2) (2008). U.S. Geological Survey Open-File Report 2007-1427H and
California Geological Survey Special Report 203H, 127 pp.
Kagan, Y. Y. and D. D. Jackson and Y. Rong (2006). A new catalog of Southern
California earthquakes, 1800-2005, Seis. Res. Lett 77, 30-38.