Abstract: Increasing vulnerability of metropolitan areas within stable continental regions (SCR), such as Memphis, TN and St. Louis, MO near the New Madrid Seismic Zone (NMSZ), to earthquakes and the very low probability level at which short term earthquake forecasting is possible make an earthquake early warning system (EEWS) a viable alternative for effective real-time risk reduction in these cities. In this study, we explore practical approaches to earthquake early warning (EEWS), and test the adaptability and potential of the real-time monitoring system in the NMSZ. We determine empirical relations based on amplitude and frequency magnitude proxies from the initial four seconds of the P-waveform records available from the Cooperative New Madrid Seismic Network (CNMSN) database for magnitude M > 2.5. The amplitude based proxies include low pass filtered peak displacement (Pd), peak velocity (Pv), and integral of the velocity squared (IV2), whereas the frequency based proxies include predominant period (tau-p), characteristic period (tau-c), and log average period (tau-log). Very few studies have considered areas with lower magnitude events. With an active EEW system in the NMSZ, damage resulting from the catastrophic events, as witnessed in 1811-1812, may be mitigated in real-time.
Poster:
Ogweno_L_Determination_of_Earthquake_early_warning_parameters_for_the_new_madrid_seismic_zone
Abstract: On 30 November 2016 at 18:25 (1st December at 00:25, UTC time) a Mw 5.5 earthquake occurred at 2.7 km depth near the town of Capellades de Alvarado, Costa Rica. It was the main shock of an earthquake sequence including foreshocks and aftershocks, located between the active volcanoes Irazú and Turrialba. This is the most recent of a series of damaging earthquakes originated in the faults crossing the Central Volcanic Range, which constitutes the northern boundary of the most populated area of the country. Using mainly the seismic records from the National Seismological Network (RSN), we present in this study a seismological analysis of the earthquake sequence and the location and characteristics of the fault that originated this seismicity. Additionally, we describe the geotectonic context of the fault and the Capellades earthquake effects. The earthquake sequence shows a clear 8-km long alignment striking north-northwest between Irazú and Turrialba volcanoes. The joint interpretation of the earthquake relocation, the main-shock moment tensor solution, and the focal mechanisms of 17 events allows for determining the source in a nearly vertical strike-slip fault, in agreement with regional active fault systems. This structure had not been previously recognized and has been named Liebres Fault in this study. The main shock was felt in most of the country, with a maximum intensity of VI+. This earthquake has been the largest in the eastern part of the Central Volcanic Range since the 1952 Patillos earthquake (Ms 5.9) and the first Mw > 5.0 earthquake recorded by the RSN in the Turrialba volcano edifice. Despite the proximity to this active volcano, which has been erupting periodically since 2010, there were no immediate eruptive effects.
Poster:
Linkimer_etal_Capellades_SSA_2018
Abstract: Crustal structure is an important parameter in global and regional seismic studies. A widely used method to obtain important features of the crust and upper mantle is receiver function, that uses teleseismic data (in distances raging from 30 to 95 degrees). In Brazil it began to be utilized since 1993, however there is still a lack of information in some areas, where the results obtained show a poor lateral resolution and great uncertainties due local complications and density of stations, as in the area of Pantanal and Chaco basin. In order to obtain more detailed crustal information about theses areas and update the map of Brazilian crust thickness, we used data of 1452 teleseismic events occurred from 2010 to 2016, registered at 166 RSBR (Brazilian Seismographic Network) and XC (FAPESP 3-basins project) stations. Automated selection of traces is performed based on azimuth recovering, radial SNR values and fit percentage of the original trace recovering. Deconvolution of the signal were done in time domain using low frequencies, a move-out correction was made for each phase and the estimation of crustal thickness was performed on receiver function traces by the Zhu and Kanamori modified method. Results shows a thin crust of 32 km +/- 1.2 km in Pantanal basin and a thicker crust in Chaco basin (37 km +/- 4 km), we also found unreliable results in the Amazon area. These new results corroborate the pre-existent models of crustal thickness in the most studied area of the eastern part of South America.
Poster:
Carolina_Rivadeneyra
Abstract: Tropical cyclones (hurricanes and typhoons) are mostly atmospheric phenomena but they also generate significant ground motions in the solid earth when they become strong. Previous studies have shown it is possible to track and monitor hurricanes that pass through dense seismic networks on land (Tanimoto and Valovcin, 2015). This limits the amount of hurricanes available to study, and so the next step is to study them while they are still out over the ocean. In this study we looked at Atlantic hurricanes from 2011 to 2016. We perform a backprojection of 0.2 Hz P waves recorded at a network of Southern California stations for the durations of the hurricanes. For many of the hurricanes in this time span, the peak amplitudes of the 0.2 Hz waves occur near the reported locations of the storms and track them through time, although the peak is off-set from the center of the hurricane. The off-set is likely a result of wave interaction between ocean waves and waves excited by the hurricane winds. It appears that the strength of the hurricane also contributes to whether or not a peak is observed. For many of the storms there is only a clear associated peak when the storm (and wind speeds) were stronger. We do not tend to observe a peak for less intense cyclones that do not reach hurricane strength winds.
Slidecast:
https://vimeo.com/277185486
Abstract: Over the past six years, the U.S. Ocean Bottom Seismograph Instrument Pool has undertaken a wide range of experiments. These experiments have addressed diverse scientific objectives through the deployment of instruments at different scales, geometries, water depths, and seasons. Overall, the experiments have been characterized by excellent instrument return rates, generally high data return, and an evolving set of instrument capabilities. These recent experiments provide insight and motivation for developments in areas such as instrument emplacement, deployment duration, communications (continuous or periodic), and standardized design elements – all key capabilities for future large-scale and/or long-term geophysical projects. Thus, we examine the characteristics, performance, and results of OBS experiments that have been done over the past six years as a key to understanding and motivating future technical directions for this important capability.
Poster:
OBSIP_Poster_Insights
Abstract: Rapid determination of earthquake magnitude is of importance for estimating shaking damages, and tsunami hazards. However, due to the complexity of source process, accurately estimating magnitude for great earthquakes in minutes after origin time is still a challenge. A recent example is the 2011 M9.0 Tohoku, Japan earthquake. We developed an approach that was originated from Hara[2007], estimating magnitude by considering P-wave displacement and source duration. The source duration is estimated using array data from regional seismic network (Hi-net). We applied this method to determine the magnitudes of large earthquakes (M >= 7) in and around Japan using seismic stations in China. Our results show the magnitudes of tested earthquakes are well determined in 5-10 min after the Origin times, with uncertainties of ±0.2. Thus, this magnitude scale may be a promising aid for disaster mitigation right after a damaging earthquake, especially when dealing with the tsunami evacuation and emergency rescue.
Poster:
2018_JpGU_Japan_earthquake_Yao
