Ground motion models for shallow crustal and deep earthquakes in Hawaii and analyses of the 2018 M 6.9 Kalapana sequence

The damaging 4 May 2018 M 6.9 Kalapana earthquake and its aftershocks have provided the largest suite of strong motion records ever produced for an earthquake sequence in Hawaii exceeding the number of records obtained in the deep 2006 M 6.7 Kiholo Bay earthquake. These records provided the best opportunity to understand the processes of strong ground shaking in Hawaii from shallow crustal (< 20 km) earthquakes. There were four foreshocks and more than 100 aftershocks of M 4.0 and greater recorded by the seismic stations. The mainshock produced only a modest horizontal peak ground acceleration (PGA) of 0.24 g at an epicentral distance of 21.5 km. In this study, we evaluated the 2018 strong motion data as well as previously recorded shallow crustal earthquakes on the Big Island. There are still insufficient strong motion data to develop an empirical ground motion model (GMM) and so we developed a GMM using the stochastic numerical modeling approach similar to what we had done for deep Hawaiian (>20 km) earthquakes. To provide inputs into the stochastic model, we performed an inversion to estimate kappa, stress drops, Ro, and Q(f) using the shallow crustal earthquake database. The GMM is valid from M 4.0 to 8.0 and at Joyner–Boore (RJB) distances up to 400 km. Models were developed for eight VS30 (time-averaged shear-wave velocity in the top 30 m) values corresponding to the National Earthquake Hazards Reduction Program (NEHRP) site bins: A (1500 m/s), B (1080 m/s), B/C (760 m/s), C (530 m/s), C/D (365 m/s), D (260 m/s), D/E (185 m/s), and E (150 m/s). The GMM is for PGA, peak horizontal ground velocity (PGV), and 5%-damped pseudo-spectral acceleration (SA) at 26 periods from 0.01 to 10 s. In addition, we updated our GMM for deep earthquakes (>20 km) to include the same NEHRP site bins using the same approach for the crustal earthquake GMM.

110th Anniversary of the Mexican National Seismological Service: An Account of Its Early Contributions

The Mexican National Seismological Service (SSN) was founded on 5 September 1910, in response to commitments made by Mexico to the International Association of Seismology in 1903. The first seismic instruments installed in 1904 were a Bosch–Omori seismograph and a Palmieri seismoscope. The SSN was formally inaugurated on 5 September 1910, a few days before the revolution broke out; a political struggle that lasted over two decades. The SSN was inaugurated with a central station in Tacubaya, Mexico City, and two secondary stations. Wiechert seismographs were selected by the SSN for its budding network. Despite the adverse economic and political situation, the SSN managed to grow and install more stations during the turmoil. Besides the installation of new seismic stations and reporting the location and macroseismic data of earthquakes in Mexico, the SSN staff produced remarkable reports of important earthquakes that occurred in those early years. Notable among these are the detailed reports on the 19 November 1912 and 4 January 1920 earthquakes on the Trans-Mexican volcanic belt. These reports have shaped the estimations of seismic hazard in this highly populated region of Mexico. In the first aftershock studies reported, the SSN took Wiechert instruments to the epicentral areas of a large subduction earthquake in 1907 and to the city of Xalapa, in the vicinity of the 1920 crustal earthquake. With foresight in those early years of seismology, the SSN scientists correctly attributed the 1912 earthquake to a local active fault. The seismograms collected in 1920 confirmed that it was a crustal earthquake and not an in-slab event. Lack of funding and official interest did not permit the modernization of the SSN for many decades. National interest in the Service was boosted by the 19 September 1985 destructive earthquake.