$M_{L}$ and $M_{w}$

The REDI system has routinely produced automatic estimates of moment magnitude ($M_{w}$) for many years. However, wary of complications caused by the publication of multiple magnitudes, these estimates were not routinely used as the ``official" magnitude until after the 05/14/2002 Gilroy earthquake ($M_{w}$ 4.9, $M_{L}$ 5.1). Since then, solutions that meet a minimum quality criterion are automatically reported (a variance reduction of 40% or higher). This criterion appears to work very well and screens out events contaminated by teleseisms. Over the last few years, nearly all events over 4.5 have met this criterion, as have a number of events in the M3.5-4.5 range. As part of the effort to establish a statewide magnitude reporting hierarchy, we have looked more closely at the estimates of $M_{w}$ (Gee et al., 2003b; 2004) and the comparison between $M_{w}$ and $M_{L}$.

Two methods of determining regional moment tensor (RMT) solutions were originally part of the REDI system - the complete waveform modeling technique (CW) of Dreger and Romanowicz (1994) and the surface wave inversion (SW) of Romanowicz et al. (1993). In FY05/06, processing for the SW algorithm was discontinued, however CW moment tensors continue to be calculated, reviewed and reported. Comparison between the results of the CW method and other regional moment tensor studies in northern California and the western United States show excellent agreement in the estimate of seismic moment and $M_{w}$.

As we transition toward statewide reporting of earthquake information, a comparison of magnitudes calculated for Southern and Northern California becomes important. We have collected a set of events recorded well by digital broadband and and strong motion stations of the Northern California (NC), Berkeley (BK) and Southern California (CI) networks and are assessing the computation of local magnitude for each station. Reseacrh Study 2.13. reports on these activities.


Table 3.19: Moment tensor solutions for significant events from July 1, 2006 through June 30, 2007 using a complete waveform fitting inversion. Epicentral information is from the UC Berkeley/USGS Northern California Earthquake Management Center. Moment is in dyne-cm and depth is in km.

Location Date UTC Time Lat. Lon. MT $M_l$ $M_w$ Str. Dip Rake Mo
Depth
Offshore of Fort Ross 7/6/2006 20:43:24 38.508 -123.463 5 3.7 3.7 4.69E+21 295 46 84
Petrolia 7/19/2006 11:41:43 40.281 -124.426 30 4.7 5 3.53E+23 102 83 173
Glen Ellen 8/3/2006 3:08:12 38.363 -122.589 5 4.7 4.4 5.64E+22 256 86 19
Bishop 9/7/2006 1:38:59 37.31 -118.284 8 3.6 3.4 1.86E+21 342 86 158
Willits 9/26/2006 20:56:13 39.31 -123.217 8 3.9 3.9 9.52E+21 333 61 -171
Petrolia 10/17/2006 20:53:18 40.55 -126 11 4.9 4.8 2.03E+23 277 85 -166
Geysers 10/20/2006 17:00:08 38.867 -122.7873 5 4.5 4.6 9.88E+22 254 68 -39
Geysers 10/20/2006 23:31:39 38.867 -122.783 5 4.5 3.8 6.50E+21 240 55 -65
Petrolia 10/24/2006 14:26:43 40.403 -125.066 5 4 4.4 4.50E+22 99 85 182
Willits 11/9/2006 8:38:13 39.355 -123.285 8 4 4 1.49E+22 336 87 172
Willits 11/10/2006 5:05:56 39.357 -123.282 8 3.7 3.7 4.69E+21 329 90 -167
Paso Robles 11/30/2006 4:06:40 35.631 -120.754 8 4.7 3.8 5.33E+21 245 89 7
Coalinga 12/16/2006 6:14:05 36.174 -120.292 5 4.3 4.2 2.16E+22 299 71 89
Petrolia 12/17/2006 15:13:40 40.392 -125.023 5 3.9 4.3 3.57E+22 274 90 -159
Bishop 12/19/2006 15:21:42 37.493 -118.188 5 4 3.7 4.33E+21 221 86 -27
Berkeley 12/21/2006 3:12:28 37.86 -122.237 8 3.7 3.6 2.85E+21 49 80 -14
Berkeley 12/23/2006 6:49:57 37.862 -122.237 11 3.7 3.6 2.82E+21 139 89 -153
Berkeley 12/23/2006 17:21:15 37.861 -122.235 11 3.5 3.4 1.63E+21 148 86 -169
Glen Ellen 1/12/2007 11:27:50 38.391 -122.615 11 3.8 3.7 3.27E+23 236 89 34
Bishop 1/17/2007 14:01:08 37.408 -118.531 5 4 3.6 3.66E+21 37 83 17
Morgan Hill 1/17/2007 17:43:22 37.12 -121.523 8 3.5 3.4 1.38E+21 328 89 -159
Petrolia 1/24/2007 13:42:52 40.312 -124.584 18 3.7 4.4 5.05E+22 187 85 25
San Simeon 2/20/2007 16:46:13 35.78 -121.382 8 3.7 3.7 4.96E+21 151 59 137
Berkeley 2/24/2007 23:46:15 37.865 -122.241 11 3.4 3.3 1.15E+21 154 88 -176
Ferndale 2/26/2007 12:19:54 40.647 -124.864 8 5 5.4 1.48E+24 60 89 -4
Lafayette 3/2/2007 4:40:00 37.901 -122.098 14 4.4 4.2 2.77E+22 82 89 -1
Bridgeport 3/9/2007 3:17:32 38.428 -119.367 11 5 4.7 1.29E+23 349 65 -114
Petrolia 4/5/2007 22:54:29 40.311 -124.578 18 3.8 4.1 1.93E+22 12 88 18
Ferndale 4/7/2007 23:55:03 40.616 -124.753 18 3.7 4.1 2.00E+22 256 78 21
Geysers 4/24/2007 21:08:28 38.796 -122.794 5 4.4 4.4 4.62E+22 342 82 -160
Geysers 4/30/2007 15:51:28 38.82 -122.823 5 3.1 3.7 3.89E+21 136 58 -133
Markleeville 4/30/2007 21:57:32 38.72 -119.62 5 3.5 3.1 5.66E+20 226 87 47
Petrolia 5/9/2007 7:50:05 40.376 -125.014 11 5 5.2 7.81E+23 188 85 24
Bishop 5/26/2007 8:04:12 37.416 -118.525 8 3.5 3.3 1.24E+21 59 81 10
Mammoth 6/12/2007 7:22:36 37.5425 -118.8677 11 3.6 3.6 3.14E+21 140 82 -143
Mammoth 6/12/2007 7:23:43 37.539 -118.876 14 5.1 4.6 9.96E+21 310 82 172
Offshore of McKinleyville 6/25/2007 2:32:25 41.1155 -124.825 18 5 5 3.36E+23 128 84 160


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