When color theory meets seismology: Principled visualization design for seismic hazard maps

<p>Probabilistic seismic hazard estimates are a key ingredient of earthquake risk mitigation strategies and are usually communicated through seismic hazard maps. Though evidence exists that visual design properties are key for effective communication using such maps, few authors describe their approach in visualizing seismic hazard. Current maps use colors, legends and data classification schemes which are suboptimal, from the visualization perspective. As such, they have the danger of miscommunicating seismic hazard. We present a set of principles regarding color choice, legend design, and classification of the continuous hazard estimate for categorical mapping. These principles are based on (1) communication goals for the seismic hazard phenomenon, (2) empirically-validated recommendations from the visualization literature and (3) other best practices in map design. We discuss the process of redesigning the German seismic hazard map using these principles. A set of prototype maps adhering to these principles are presented. We also describe ongoing efforts to test the redesigned maps, as well as how to use them to further communicate the uncertainty around probabilistic hazard estimates.</p>

Precedent-extrapolation estimate of the seismic hazard in the Sakhalin and the Southern Kurils region

The paper describes the algorithm and the results of the seismic hazard estimate in the Sakhalin and Southern Kurils region based on the data of the Japan Regional Catalogue (JMA). A nonlinear differential equation of the second order is used as a mathematical model, and algorithms for optimization and predictability estimation are presented by the author's solutions. The forecasting algorithm is based on the search for seismic activity zones in which the current activity trends correspond to foreshock sequences recorded before strong earthquakes (precedents) that have already occurred. The earthquake time is calculated with extrapolating the detected trends to the level of activity that occurred at the time of the precedent earthquake. By the example of precedent foreshock sequences in Japan, it is shown that the lead time of such a forecast reaches 10–15 years and its implementation is due to the preservation and stability of the identified trends. A map of potentially dangerous zones for Sakhalin and the Kuril Islands and some examples of calculating the time of strong earthquakes according to the JMA catalogue as of August 31, 2018 are presented. Action sequence in identifying the potentially dangerous trends in seismic activity and the specifics of possible use of the technique in the Sakhalin region are considered.

New prototype of 6-component seismograph Rotaphone CY: laboratory testing and pilot measurements

<p><span>Rotaphones are seismic sensor systems consisting of parallel pairs of geophones attached to a rigid frame anchored to ground. Such an arrangement allows to measure both translational and rotational ground motions. Translations are measured by individual geophones while rotations are determined using differential records from the paired geophones. The individual geophones are calibrated simultaneously with each measurement utilizing overdetermined rotational components. A new prototype, Rotaphone CY has been recently developed. The design has been improved taking into account experience with field measurements performed using older prototypes. The device is optimized for recording weak ground motions from local microearthquakes, both natural or induced, in a high-frequency range. The instruments were carefully tested in laboratory conditions. Tests were followed by pilot field deployments in various places in the Czech Republic. A local network of six Rotaphones CY has been deployed in the scope of Litomerice geothermal project to investigate induced seismicity related to the production of geothermal energy. The instrument has also been recently deployed at the nuclear power plant Dukovany to monitor local seismicity with the aim to improve seismic hazard estimate. A small-aperture array of four these instruments was installed at the Geophysical Observatory Fürstenfeldbruck, Germany, in the frame of a comparative rotation sensors experiment. Examples of 6-component records from these pilot measurements are shown.</span></p>

A test for checking earthquake aperiodicity estimates from small samples

In recent years, many new models for earthquake recurrence were proposed. Some are focusing on the clustering properties on a small time scale, while others try to model the long term behavior of large mainshocks. To this last purpose, there is a growing interest for models that take into account the aperiodicity aiming to a time-dependent hazard estimate. It is well known that a limited number of inter-event times (IETs) may lead to biased values of the distribution parameters. To overcome this problem different solutions were proposed. This paper focuses on two of them: Monte Carlo simulation of the process and aperiodicity estimated via a statistical proxy. The topics discussed are: 1) how many IETs are needed for a correct estimate, 2) to which extent a Poisson distribution is equally able to describe the process, 3) the influence of errors associated to paleoseismological IETs, and 4) the goodness of the success ratio from simulations. A simple test is proposed to discriminate real aperiodicity from apparent aperiodicity coming from undersampling.