Contemporary Earthquake Hazards in the West-Northwest Himalaya: A Statistical Perspective through Natural Times

Abstract

Himalayan earthquakes have deep societal and economic impact. In this article, we implement a surrogate method of nowcasting (Rundle et al., 2016) to determine the current state of seismic hazard from large earthquakes in a dozen populous cities from India and Pakistan that belong to the west-northwest part of Himalayan orogeny. For this, we (1) perform statistical inference of natural times, intersperse counts of small-magnitude events between pairs of succeeding large events, based on a set of eight probability distributions; (2) compute earthquake potential score (EPS) of 14 cities from the best-fit cumulative distribution of natural times; and (3) carry out a sensitivity testing of parameters—threshold magnitude and area of city region. Formulation of natural time (Varostos et al., 2005) based on frequency–magnitude power-law statistics essentially avoids the daunting need of seismicity declustering in hazard estimation. A retrospective analysis of natural time counts corresponding to M≥6 events for the Indian cities provides an EPS (%) as New Delhi (56), Chandigarh (86), Dehradun (83), Jammu (99), Ludhiana (89), Moradabad (84), and Shimla (87), whereas the cities in Pakistan observe an EPS (%) as Islamabad (99), Faisalabad (88), Gujranwala (99), Lahore (89), Multan (98), Peshawar (38), and Rawalpindi (99). The estimated nowcast values that range from 38% to as high as 99% lead to a rapid yet useful ranking of cities in terms of their present progression to the regional earthquake cycle of magnitude ≥6.0 events. The analysis inevitably encourages scientists and engineers from governments and industry to join hands for better policymaking toward land-use planning, insurance, and disaster preparation in the west-northwest part of active Himalayan belt.

Estimating the Epicenter of an Impending Strong Earthquake by Combining the Seismicity Order Parameter Variability Analysis with Earthquake Networks and Nowcasting: Application in the Eastern Mediterranean

“…To achieve this determination, one uses an EQ catalog to calculate from the 'small' EQs, which are defined as those with magnitude M < M λ , but above a threshold M σ , i.e., of magnitude M ∈ [M σ , M λ ), the level of hazard for 'large' M ≥ M λ EQs. The lower threshold M σ is typically the completeness threshold of the EQ catalog used [33], while the EQ catalogs employed [33,116,116,117,123,124,136] are global seismic catalogs such as the Advanced National Seismic System Composite Catalog or the NEIC PDE catalog. For such global catalogs, a M σ = 4.0 magnitude threshold was considered [116,117] for applications in EQ-prone areas outside the United States, such as those in Greece, Japan, and India.…”

“…and is a measure of the level of current hazard, see Figure 3a. In References [33,116,117,123,136], the seismic risk for various cities of the world was estimated through the following procedure: After calculating the CDF Prob[n < n(t)] within a large area, the number ñ of the small EQs around a city, i.e., those occurring within a circular region of epicentral distances r < R since the occurrence of the last strong EQ in this circular region, was found. Given that EQs exhibit ergodicity-see, e.g., References [58,137,138]-Rundle et al [117] suggested that the seismic risk around a city can be estimated by using the EPS corresponding to the current value of ñ by inserting n(t) = ñ in Equation (6).…”

“…It is the scope of the present paper to show that by combining the above two NTA results with the modern method of nowcasting EQs [33], an estimate of the epicenter of the impending EQ with M ≥ 7.1 in the eastern Mediterranean region is achieved. EQ nowcasting employs natural time, which is unique in its characteristics [116], to estimate seismic risk by means of an EQ potential score (EPS) and found many useful applications, both regionally and globally [33,[116][117][118][119][120][121][122][123][124][125][126]. EQ nowcasting [33] has, so far, focused on describing the current state of fault systems.…”

Nowcasting Earthquakes in Sulawesi Island, Indonesia

“…(Pasari & Sharma, 2020). The frequency-magnitude statistics of five different time periods of earthquake catalog illustrate that the b-value estimates are generally homogeneous in the time domain.…”

“…Under this set up, the nowcasting method describes the seismic progression of a region in terms of earthquake potential score (EPS) measured through the cumulative probability for the current event counts (Rundle et al, 2016(Rundle et al, , 2018Pasari, 2019). The method has been successfully applied to several seismogenic cities such as Ankara, Dhaka, Islamabad, Kolkata, Lima, Manila, New Delhi, Taipei, Tokyo, Los Angeles and San Francisco (Rundle et al, 2016;Pasari, 2019;Pasari & Sharma, 2020).…”