Transtensional Rupture within a Diffuse Plate Boundary Zone during the 2020 Mw 6.4 Puerto Rico Earthquake

On 7 January 2020, an Mw 6.4 earthquake occurred in the northeastern Caribbean, a few kilometers offshore of the island of Puerto Rico. It was the mainshock of a complex seismic sequence, characterized by a large number of energetic earthquakes illuminating an east–west elongated area along the southwestern coast of Puerto Rico. Deformation fields constrained by Interferometric Synthetic Aperture Radar and Global Navigation Satellite System data indicate that the coseismic movements affected only the western part of the island. To assess the mainshock’s source fault parameters, we combined the geodetically derived coseismic deformation with teleseismic waveforms using Bayesian inference. The results indicate a roughly east–west oriented fault, dipping northward and accommodating ∼1.4 m of transtensional motion. Besides, the determined location and orientation parameters suggest an offshore continuation of the recently mapped North Boquerón Bay–Punta Montalva fault in southwest Puerto Rico. This highlights the existence of unmapped faults with moderate-to-large earthquake potential within the Puerto Rico region.

Estimating the Epicenter of a Future Strong Earthquake in Southern California, Mexico, and Central America by Means of Natural Time Analysis and Earthquake Nowcasting

It has recently been shown in the Eastern Mediterranean that by combining natural time analysis of seismicity with earthquake networks based on similar activity patterns and earthquake nowcasting, an estimate of the epicenter location of a future strong earthquake can be obtained. This is based on the construction of average earthquake potential score maps. Here, we propose a method of obtaining such estimates for a highly seismically active area that includes Southern California, Mexico and part of Central America, i.e., the area N1035W80120. The study includes 28 strong earthquakes of magnitude M ≥7.0 that occurred during the time period from 1989 to 2020. The results indicate that there is a strong correlation between the epicenter of a future strong earthquake and the average earthquake potential score maps. Moreover, the method is also applied to the very recent 7 September 2021 Guerrero, Mexico, M7 earthquake as well as to the 22 September 2021 Jiquilillo, Nicaragua, M6.5 earthquake with successful results. We also show that in 28 out of the 29 strong M ≥7.0 EQs studied, their epicenters lie close to an estimated zone covering only 8.5% of the total area.

Analysis of Tsunami Wave Height, Run-up, and Inundation in The Coastal of Blitar and Malang Regency

Indonesia is an archipelago located at the meeting point of 3 tectonic plates which constantly collide over time, the energy due to the collision will accumulate and be able to cause large earthquakes that can generate tsunamis. The island of Java is in the subduction zone of these plates, which causes the southern part of Java to have a high earthquake potential. On April 10, 2021, an earthquake measuring M 6.1 occurred in the south of Blitar and Malang. This earthquake was felt by most of the people of East Java, If the earthquake is large enough, it can cause a tsunami on the southern coast of East Java. Therefore, modeling was carried out using the FLOW module of Delft3D software while using earthquake parameters with a strength of M 9.1 which is the worst possible scenario on the southern coast of East Java. The results of this study indicate the fastest tsunami arrival time is 21 minutes, the highest maximum tsunami height is 20 meters, the highest run-up reaches 17,5 meters, and the furthest inundation reaches 765 meters along the southern coast of Blitar and Malang Regency.

Crustal deformation of Eastern Indonesia regions derived from 2010-2018 GNSS Data

Eastern Indonesia lies in a complex tectonic region due to the interaction of four major tectonic plates: the Australian Plate, Pacific Plate, Philippine Sea Plate, and Sunda Block. Therefore, this region hosted some destructive seismic activities as well as tectonic deformation, such as the Mw 7.5 Palu Earthquake, the sequences of the 2018 Lombok Earthquake, and the Mw 6.5 Ambon Earthquake in 2019. Our work proposes a recent study on crustal deformation in Eastern Indonesia inferred from Global Positioning System (GPS) velocity field. We used GPS data from the observations of 49 permanent and 61 campaign stations from 2010 to 2018. Here, our velocity field result represents long-term tectonic deformation regions in Eastern Indonesia continuously, from Bali in the west to Papua in the east, demonstrated both in the ITRF 2008 and the Sunda reference frames. The spatial pattern of velocity field map collected from this research will give an initial insight into the present-day tectonic condition in Eastern Indonesia and then can be used to improve our ability to assess this area’s earthquake potential.

Nowcasting earthquakes in Sulawesi Island, Indonesia

Large devastating events such as earthquakes often display frequency–magnitude statistics that exhibit power-law distribution. In this study, we implement a recently developed method called earthquake nowcasting (Rundle et al. in Earth Space Sci 3: 480–486, 2016) to evaluate the current state of earthquake hazards in the seismic prone Sulawesi province, Indonesia. The nowcasting technique considers statistical behavior of small event counts between successive large earthquakes, known as natural times, to infer the seismic progression of large earthquake cycles in a defined region. To develop natural-time statistics in the Sulawesi Island, we employ four probability models, namely exponential, exponentiated exponential, gamma, and Weibull distribution. Statistical inference of natural times reveals that (i) exponential distribution has the best representation to the observed data; (ii) estimated nowcast scores (%) corresponding to M ≥ 6.5 events for 21 cities are Bau-bau (41), Bitung (70), Bone (44), Buton (39), Donggala (63), Gorontalo (49), Kendari (27), Kolaka (30), Luwuk (56), Makassar (52), Mamuju (58), Manado (70), Morowali (37), Palopo (34), Palu (62), Pare-pare (82), Polewali (61), Poso (42), Taliabu (55), Toli-toli (58), and Watampone (55); and (iii) the results are broadly stable against the changes of magnitude threshold and area of local regions. The presently revealed stationary Poissonian nature of the underlying natural-time statistics in Sulawesi brings out a key conclusion that the seismic risk is the same for all city regions despite their different levels of cycle progression realized through nowcast scores. In addition, though the earthquake potential scores of the city regions will be updated with the occurrence of each small earthquake in the respective region, the seismic risk remains the same throughout the Sulawesi Island.

Late Quaternary faulting in southern Matese (central Italy): implications for earthquake potential in the southern Apennines

We studied in detail the Gioia Sannitica active normal fault (GF) along the Southern Matese Fault system in the southern Apennines of Italy. The current activity of the fault system and its potential to produce strong earthquakes have been underestimated so far, and are now defined. Precise mapping of the GF fault trace on a 1 : 20,000 geological map and several point data on geometry, kinematics and throw rate are made available in electronic format. The GF, and in general the entire fault system along the southern Matese mountain front, is made of slowly-slipping faults, with a long active history revealed by the large geologic offsets, mature geomorphology, and complex fault pattern and kinematics. Present activity has resulted in Late Quaternary fault scarps resurrecting the foot of the mountain front, and Holocene surface faulting. The slip rate varies along-strike, with maximum Late Pleistocene – Holocene throw rate of ~0.5 mm/yr. Activation of the 11.5 km-long GF can produce up to M 6.1 earthquakes. If activated together with the 18 km-long Ailano-Piedimonte Matese fault (APMF), the seismogenic potential would be M 6.8. The slip history of the two faults is compatible with a contemporaneous rupture. The observed Holocene displacements on the GF and APMF are compatible with activations during some poorly known historical earthquakes, such as the 1293 (M 5.8), 1349 (M 6.8; southern prolongation of the rupture on the Aquae Iuliae fault?) and CE 346 earthquakes. A fault rupture during the 847 poorly-constrained historical earthquake is also compatible with the dated displacements.