The Dead Sea Fault (DSF) is a plate-boundary where large earthquakes are expected and largely overdue due to the lack of such events in the instrumental era. Sequences of earthquakes along the DSF are documented by historical evidence, one of the most devastating occurred in the mid-8th century CE. Here we describe site-specific archaeoseismological observations at the ancient Tiberias city, on the western shore of the Sea of Galilee. We map Roman and Byzantine relics faulted in the mid-8th century CE by a pure normal fault. We use geophysical, geomorphological and structural analyses integrated with published data, to assess the seismic hazard of the Jordan Valley Western Boundary Fault (JVWB). We propose that the normal JVWB can rupture the surface along its ~45 km trace running from Tiberias toward the S crossing Bet Shean, Tel Rehov and Tel Teomim. The JVWB, parallel to the main strike-slip Jordan Valley Fault segment, might be regarded as a major earthquake source in this region. We test the hypotheses of both single fault and multi-faults rupture scenarios, which result in an expected range of Mw from 6.9 (single rupture of the JVWB) to 7.6 (multiple rupture of the JVWB and Jordan Valley Fault). Our results suggest that seismic source characterization in the Sea of Galilee region must include normal faults capable of surface rupturing, despite the absence of such events in the instrumental catalogue.

Strong (M 6 - 7) to large (M 7 – 8) earthquakes are capable to produce surface faulting both along the primary fault and distributed faults. The availability of modern technologies clearly highlighted the complexity of surface faulting associated with recent earthquakes worldwide, providing a dataset with unprecedented detail. Surface faulting and deformation pose a threat for critical facilities, lifelines and infrastructures; the assessment of the probability of occurrence of fault displacement is thus vital for risk mitigation and a proper planning. The recent datasets were not yet analyzed in this perspective, and current methodologies and scaling relations rely on data acquired few to tens of years ago. We perform a probabilistic fault displacement hazard analysis on distributed faulting due to modern earthquakes with normal and strike-slip kinematics. We show that current scaling relations tend to underpredict the actual occurrence of faulting, and we propose updated relations. Distributed faulting due to a large earthquake on one hand, and repeated ruptures at the same spot in a short time interval (e.g., Central Italy, 2016; Searles Valley and Ridgecrest 2019) on the other hand, are the end-members of a spectrum of surface faulting behavior. If not taken into account during the interpretation of paleoseismological data, different modes of fault rupture can significantly bias the derived earthquake parameters and, consequently, inferences on the regional tectonic activity.

The 2020 Monte Cristo Earthquake sequence in western Nevada began with a M6.5 shock on 5/15/20, and was the largest to occur in Nevada since 1954. The event exhibited left-lateral slip along an eastward extension of the Candelaria fault and extensive distributed surface faulting in the epicentral area. Groundwater monitoring and strain analysis were conducted to evaluate hydrochemical effects on the regional groundwater systems following the initial event. Physio-chemical monitoring, (started on 5/16 and still ongoing) includes measurements of temperature (temp), pH, specific conductance (SpC), flow rate, alkalinity and collection of samples for major ions and trace element analysis. Since sites had not been monitored prior to the initial shock, measurements were evaluated against a year of post-event data to gauge response to seismicity. Four sites were monitored: a well from Columbus Marsh (CM) located 5 km from the epicenter; an artesian thermal well from Fish Lake Valley (FL); a well at Willow Ranch (WR) tapping cool water above the FL waters; and a spring along Mina Dump Road (MD) located 15 km north of the Candelaria fault on the Benton Springs Fault. GPS and InSAR measurements were used to create a model of the slip from which we estimated coseismic strain at each sampling location. All but one sample site, MD, experienced positive dilation and CM experienced the greatest amount of strain (15-17 microstrains). Hydrologic and chemical changes were observed following the initial shock, varying between sites. CM had significantly lower SpC values in the week following the event, as well as changes in major ion composition. Other sites showed minor changes; MD showed fluctuations in pH values and FL experienced a slight drop in temp. These waters showed minimal changes in major ions and trace elemental composition. Clear responses were observed throughout three >M5 aftershocks (6/30/20, 11/13/20, and 12/1/20), especially in SpC and alkalinity. A remarkable change in elemental concentration (an increase in Ca, K, SO4, Fe, and decrease in Na, Cl, Li, and Ba) was observed in CM. WR experienced a transient increase in temp measured two weeks prior to the 11/13/20 earthquake. Strain analyses of the smaller (>M5) events are planned to further evaluate observed responses and to clarify factors affecting groundwater response.