Abstract: In 2015, the Central American countries (Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica and Panama) agreed to establish a Central American Tsunami Advisory Center (CATAC) at INETER in Managua, Nicaragua. This proposal was also approved by the Intergovernmental Oceanographic Committee (IOC) of UNESCO and the Intergovernmental Coordination Groups (ICG) of the Pacific Ocean Tsunami Warning Systems (PTWS) and the Caribbean Sea (CARIBEEWS). CATAC will provide scientific real-time technical tsunami services related to the Pacific Ocean and the Caribbean Sea to the Scientific Institutions and Civil Protection Agencies of the Central American countries. The issuance of tsunami advice to the population remains the responsibility of the national governments. In 2016, INETER started to establish CATAC. The Nicaraguan government agreed with the Japan International Cooperation Agency (JICA) to execute a technical assistance project to strengthen CATAC; this project began in October 2016. Progress was made in the development of the data processing system, the monitoring networks, the construction of the tsunami database, the training of personnel and the development of Standard Operating Procedures (SOP).
Poster:
2018.05_LACSC-SSA_Furukawa_etal
Abstract: The intraslab earthquake of 2017 was the second most destructive in the history of Mexico City, next only to the interplate earthquake of 1985 (Mw8.0). PGA of 59 gal at the SM station of CU, located on basalt lava flows and in continuous operation since 1964, was the largest ever, twice the PGA during the 1985 earthquake (29 gal). The 2017 earthquake has raised questions that are critical in fathoming the seismic vulnerability of the city. Was such an intraslab earthquake (Mw~7 at a hypocentral distance of 127 km) unexpected? Were the recorded ground motions in the city unusually high? Why did the damage patterns during the earthquakes of 2017 and 1985 differ? Mw~5.9 events have occurred in recent years near the 2017 earthquake. Three Mw≥6.9 earthquakes have occurred since 1964 in the distance range 184-225 km. Thus, Mw and R of the 2017 earthquake was not surprising. However, Fourier acceleration spectra at CU of 10 intraslab earthquakes with the largest PGAs, reduced to a common R=127 km, shows that the amplitudes of the 2017 events were abnormally high in 1-2 s range. With respect to site-specific GMPE, the observed PGV and Sa at 1 < T < 2 s were also anomalously high. Yet, as the recordings at 65 sites in the city attest, Sa exceeded the design spectra of Mexico City´s 1987 building code at only few sites. The intraslab earthquakes occur closer to the city, at greater depth, and involve higher stress drop than their interplate counterparts. Consequently, the ground motion is relatively enriched at high frequencies as compared to the interplate earthquakes which is dominated by lower frequency waves (f < 0.5 Hz). This explains the observed difference in the damage pattern during 2017 and 1985. The damage during 2017 occurred at sites with a natural period, Ts, between 0.5 and 2 s; during 1985 the damage was concentrated at sites with 1.6 < Ts < 3 s. This damage pattern will, no doubt, repeat in the city during future strong intraslab and interplate earthquakes.
Media has not been submitted for this Presentation
Abstract: The recent dramatic increase in seismic events in the Central and Eastern United States is suggested to be linked to underground high-volume fluid injection. Some researchers investigated the qualitative correlation between the injection operations and induced seismicity. However, they ignored the physical process governing poroelastic fluid diffusion and earthquake nucleation. Thus, we propose a physics-based induced earthquake forecasting model which couples linear poroelasticity to rate-and-state earthquake model, considering the complex relationship between injections and consequent seismicity. Firstly, we implement a coupled flow and poroelastic model to simulate the evolution of pore pressure and poroelastic stresses in time and space. Secondly, we use local geology and maps of existing faults to calculate the rate of Coulomb failure stress change. Thirdly, we import the maps of Coulomb stress change rate into a seismicity rate model. Finally, the estimated seismicity rate changes are used within a probabilistic model to evaluate the time-dependent seismic hazard for each given fault. Both Texas and Oklahoma experienced intensive deep waste fluid injections and seismicity increases. To investigate the associated link, we apply our method to the time-varying injections at 96 Ellenberger wells in the Barnett Shale during 2007-2015 and 855 Arbuckle wells in Oklahoma during 1995-2017. In both study areas, earthquake locations correlate well with pore pressure and poroelastic stress, although poroelastic stress is smaller than pore pressure. Given the good quality of earthquake record in Oklahoma, the predicted earthquake magnitude-time distribution shows excellent fit to observation, confirming the performance of the model. The obtained time-dependent seismic hazard is spatiotemporally heterogeneous. Decreasing injection rates does not necessarily reduce probabilities immediately. The presented framework can be used for operational induced earthquake forecasting.
Slidecast:
https://vimeo.com/276910745
Abstract: The September 8th 2017, Mw8.2 earthquake offshore Chiapas, Mexico, is the largest earthquake recorded history in Chiapas since 1902. It caused damage in the states of Oaxaca, Chiapas and Tabasco. This earthquake, a deep intraplate event on a normal fault on the oceanic subducting plate, generated a tsunami recorded at several tide gauge stations in Mexico and on the Pacific Ocean. We covered ground observations along 41 km of the coast of Chiapas, encompassing the 8 sites with the highest projected wave heights based on our preliminary tsunami model (maximum tsunami amplitudes between -94.5 and -93.0 W). The maximum runup was ~3 m at Boca del Cielo, and maximum inundation distance was 190 m in Puerto Arista, corresponding to the coast directly opposite the epicenter and in the central sector of the Gulf of Tehuantepec. In general, our field data agree with the predicted results from the preliminary tsunami model. Tsunami scour and erosion, and lateral spreading was evident on the Chiapas coast. Tsunami deposits, mainly sand, reached up to 32 cm thickness thinning landwards up to 172 m distance. We collected information regarding the tsunami early warning system as part of eyewitness interviews during the post-tsunami survey. Even though the Mexican tsunami early warning system (CAT) issued several warnings, the tsunami arrival struck the Chiapas coast prior to the arrival of official warnings to the residents of small coastal towns, owing to the multi-ranked notification system. Thus, a tsunami early warning system with a direct warning to all coastal communities is needed. Some people evacuated under their own initiative, indigenous Ikoot community though were self-organized, calling people to move to higher ground, but some did not evacuate. Tsunami educational material has been produced in different languages and made available online however, its distribution has not been effective. Therefore, community-based education and awareness programs are needed.
Slidecast:
https://vimeo.com/276507426
Abstract: The 7.6 Mw Honduras event provided a valuable test of logistical and community preparedness for tsunamis in Puerto Rico (PR) and Virgin Islands (VI). This event provided an opportunity to quantify the extent of the continued recovery of the local emergency alert systems in Puerto Rico post Hurricanes Irma and Maria and highlighted gaps in public and emergency management knowledge. In the immediate time after the event, PR and the VI were placed under a tsunami advisory by the Pacific Tsunami Warning Center. Consequently, the Puerto Rico Seismic Network (PRSN) retransmitted this information as mandated by our mission and role as a Tsunami Warning Focal Point Alternate. Here we present and evaluate the PRSN response to the event as well as detail continued damages to the communication systems from the 2017 hurricanes detected in this response. In this poster we review the PR/VI tsunami protocol and highlight the need for more formal education on tsunami threats and responses; PRSN is planning to address this issue in the following fiscal year by providing training with evaluation metrics to ensure that local emergency managers have solid knowledge of threat levels and the appropriate response.
Slidecast:
https://vimeo.com/276507548
Abstract: Large-scale wastewater disposal has led to a fast-paced reawakening of faults in the Oklahoma/Kansas region. High resolution earthquake relocations show that the inventory of ancient basement faults in the study region differs from results of seismic surveys and geologic mapping focused on the sedimentary cover. We analyze the evolution of seismic activity in the Guthrie-Langston sequence in central Oklahoma in greater detail. Here, seismic activity has reactivated a network of at least 12 sub-vertical faults in an area less than 10 km across. Recorded activity began in late 2013 and peaked about 6 months later and includes two M4 earthquakes. These earthquakes characteristically occur at about 4 km depth below the top of the basement and do not reach the sedimentary cover. The sequence shows a radial growth pattern despite being no closer than 10 km to significant wastewater disposal activity. Hydrologic modeling suggests that activity initiated with a time lag of several years relative to early injection activity. Once initiated, earthquake interactions contribute to the propagation of seismicity along the reactivated faults. As a result, the spatio-temporal evolution of the seismicity mimics a diffusive pattern that is typically thought to be associated with injection activity. Analysis of the Fault Slip Potential shows that most faults are critically stressed in the contemporary stress field. Activity on some faults, for which we find low slip probability, suggest a significant contribution of geomechanical heterogeneities to the reawakening of these ancient basement faults.
Slidecast:
https://vimeo.com/276910577
