The M s ∼ 7.7 Sarez-Pamir earthquake of 1911 February 18 is the largest instrumentally recorded earthquake in the Pamir region. It triggered one of the largest landslides of the past century, building a giant natural dam and forming Lake Sarez. As for many strong earthquakes from that time, information about source parameters of the Sarez-Pamir earthquake is limited due to the sparse observations. Here, we present the analysis of analogue seismic records of the Sarez-Pamir earthquake. We have collected, scanned and digitized 26 seismic records from 13 stations worldwide to relocate the epicentre and determine the event's depth (∼26 km) and magnitude (m B 7.3 and M s 7.7). The unusually good quality of the digitized waveforms allowed their modelling, revealing an NE-striking sinistral strike-slip focal mechanism in accordance with regional tectonics. The shallow depth and magnitude (M w 7.3) of the earthquake were confirmed. Additionally, we investigated the possible contribution of the landslide to the waveforms and present an alternative source model assuming the landslide and earthquake occurred in close sequence.

A series of large-magnitude earthquakes above 6.9 occurred in the northern Tien-Shan between 1885 and 1911. The Chilik earthquake of 11 July 1889, has been listed with a magnitude of 8.3, based on sparse macroseismic intensities, constrained by reported damage. Despite the existence of several juvenile fault scarps in the epicentral region, that are possibly associated with the 1889 earthquake, no through-going surface rupture having the dimensions expected for a magnitude 8.3 earthquake has been located – a puzzling dilemma. Could the magnitude have been overestimated? This would have major implications not only for the understanding of the earthquake series, but also for regional hazard estimates. Fortunately, a fragmentary record from an early Rebeur–Paschwitz seismometer exists for the Chilik event, recorded in Wilhelmshaven (Germany). To constrain the magnitude, we compare the late coda waves of this record with those of recent events from Central Asia, recorded on modern instruments in Germany and filtered with Rebeur–Paschwitz instrument characteristics. Additional constraints come from disturbances of historic magnetograms that exist from the Chilik and the 1911 Chon-Kemin earthquakes. Scaling of these historic records confirm a magnitude of about 8 for the 1889 Chilik earthquake, pointing towards a lower crustal contribution to the fault area.

SUMMARY On 7 December 2015, a shallow Mw 7.2 strike-slip earthquake struck the Murghab River Valley in the Central Pamirs of Tajikistan. Seismologically this event was similar to a large seismic event in 1911 whose causative fault has never been identified. We measure the displacement field of the 2015 event from satellite observations using Sentinel-1 radar interferometry, Landsat-8 optical pixel-tracking, and surface rupture mapping from high resolution SPOT-6/7 imagery to characterize the role this earthquake rupture plays in the accommodation of strain on its causative structure, the Sarez-Karakul fault. We present geomorphic mapping and interpretations of other Quaternary-active reaches of this fault system, which highlight variable rupture history of the different sections. These sections appear to be separated by inherited bedrock structural boundaries. Significantly, the reaches of the fault northeast and southwest of the 2015 rupture exhibit the freshest morphology prior to 2015, indicative of a more recent rupture than elsewhere. Using new high resolution imagery we map fresh scarps at the northern and southern ends of the Sarez-Karakul fault which may represent this 1911 rupture. To test which of these reaches could have been the source of the elusive 1911 event, we compare synthetic seismograms from three plausible fault sources determined from geomorphology, with observed seismic traces from 1911 at early recording stations throughout Europe. We find that the best fitting fault source is in fact southwest of the 2015 rupture, meaning that we have a record of three distinct recent events on the Sarez-Karakul fault system—two of them instrumentally recorded. Our mapping of these separate events reveals a correlation between their boundaries and the active and inherited thrust and suture systems that intersect the northeast striking left-lateral fault, suggesting structural control over the extents of individual ruptures on the active strike-slip fault.

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Reported magnitudes ranging between 7.8 and 8.7 highlight a confusion about the true size of the 1920 Haiyuan earthquake, the largest earthquake recorded in the northeast Tibetan Plateau. We compiled a global data set of previously unlooked‐at historical seismograms and performed modern computational analyses on the digitized seismic records. We found the epicenter to be near Haiyuan town and obtained a moment magnitude of MW=7.9±0.2. Following traditional approaches, we obtained mB=7.9±0.3 with data from 21 stations and MS(20)=8.1±0.2 with data from three stations. Geomorphologically, we mapped the surface rupture and horizontal offsets on high‐resolution Pleiades satellite and drone imagery that covered the entire western and middle sections of the 1920 Haiyuan earthquake rupture and compiled offsets reported on the eastern section from field measurements in the 1980s. Careful discrimination between single‐event and cumulative offsets suggests average horizontal slips of 3.0±1.0 m on the western section, 4.5±1.5 m on the middle section, and 3.5±0.5 m on the eastern section, indicating a total moment magnitude of MW=7.8±0.1. Thus, the seismological and geomorphological results agree within the uncertainties, a weighted average giving a moment magnitude of MW=7.9±0.2 for the 1920 Haiyuan earthquake. It is likely that earthquake magnitudes based on the historical M were systematically overestimated.