![]() ![]() ![]() The May 2015 flooding was almost entirely produced by backwater flooding from the Blanco River whose confluence is approximately 2.2 miles southeast of downtown. 2015 was produced by overbank flooding of San Marcos River and its tributaries by spills from upstream dams. Large sections of San Marcos, TX were flooded in Oct. We also suggest that the mantle slip loads the crust eventually resulting in relatively large crustal earthquakes.īackwater Flooding in San Marcos, TX from the Blanco RiverĮarl, Richard Gaenzle, Kyle G. We hypothesize that the highly localized uppermost mantle seismicity is triggered by aseismic slow-slip of the surrounding ductile mantle. In the week leading up to the M=5.4 event we observe a significant downward migration of crustal seismicity, which results in the subsequent nucleation of the main event at the base of the crust. Two mantle sequences occurred in a small area of 3x3 km about 4 and 2 weeks before the M=5.4 event. Moreover, we observe increased seismic activity in the uppermost mantle about 30 days before the largest (M=5.4) earthquake. These sequences cannot be described by known empirical laws. The temporal distribution of crustal events follows common patterns given by Omori's law, while most mantle seismicity occurs in spatially tight sequences of unusually short durations lasting 30 minutes or less. Statistical analysis reveals striking differences between crustal and mantle seismicity. Earthquakes extend from 0 km to 20 km depth, but cluster predominantly at two depth levels: in the crust (5-7 km) and in the uppermost mantle (12-17 km). The catalog magnitude of completeness is M=2.2 with an overall b value of 1. Almost 3,000 well-constrained earthquakes were detected and located along the Blanco Ridge by an automatic procedure (using BRTT Antelope) and relocated using a relative location algorithm (hypoDD). Our research concentrates on the Blanco Ridge, a purely transform segment of the Blanco Fault Zone, that spans over 130 km between the Cascadia and the Gorda pull-apart depressions. ![]() We present results of the Blanco Transform OBS Experiment, which consists of the deployment of 55 three-component broadband and short-period ocean bottom seismometers in the vicinity of the Blanco Fault Zone for the period between September 2012 and October 2013. Mantle-crust interaction at the Blanco Ridge segment of the Blanco Transform Fault Zone: Results from the Blanco Transform Fault OBS Experiment ![]()
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