diff --git a/sfm/database.py b/sfm/database.py
index 1792f20..37d0bbb 100644
--- a/sfm/database.py
+++ b/sfm/database.py
@@ -86,6 +86,14 @@ CREATE TABLE IF NOT EXISTS events (
     a5_pickle_filename      TEXT,                   -- "<filename>.a5.pkl" sidecar
     sidecar_filename        TEXT,                   -- "<filename>.sfm.json" review/metadata sidecar
     device_family           TEXT,                   -- "series3" (MiniMate Plus / BW) | "series4" (Micromate / Thor) — drives per-family UI rendering (units, labels)
+    tran_zc_freq            REAL,                   -- Transverse ZC frequency (Hz)
+    vert_zc_freq            REAL,                   -- Vertical ZC frequency (Hz)
+    long_zc_freq            REAL,                   -- Longitudinal ZC frequency (Hz)
+    mic_zc_freq             REAL,                   -- Microphone ZC frequency (Hz)
+    tran_zc_above_range     INTEGER,                -- 1 = value is device ceiling, render ">N Hz"
+    vert_zc_above_range     INTEGER,
+    long_zc_above_range     INTEGER,
+    mic_zc_above_range      INTEGER,
     created_at              TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
     UNIQUE(serial, timestamp)
 );
@@ -200,6 +208,14 @@ class SeismoDb:
             ("a5_pickle_filename", "TEXT"),
             ("sidecar_filename",   "TEXT"),
             ("device_family",      "TEXT"),
+            ("tran_zc_freq",        "REAL"),
+            ("vert_zc_freq",        "REAL"),
+            ("long_zc_freq",        "REAL"),
+            ("mic_zc_freq",         "REAL"),
+            ("tran_zc_above_range", "INTEGER"),
+            ("vert_zc_above_range", "INTEGER"),
+            ("long_zc_above_range", "INTEGER"),
+            ("mic_zc_above_range",  "INTEGER"),
         ):
             if col not in existing_cols:
                 log.info("_migrate: events ADD COLUMN %s %s", col, ddl)
diff --git a/tests/test_zc_freq_columns.py b/tests/test_zc_freq_columns.py
new file mode 100644
index 0000000..51b079f
--- /dev/null
+++ b/tests/test_zc_freq_columns.py
@@ -0,0 +1,45 @@
+from __future__ import annotations
+import os, sys, sqlite3
+from pathlib import Path
+import pytest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+from sfm.database import SeismoDb
+
+ZC_COLS = ["tran_zc_freq", "vert_zc_freq", "long_zc_freq", "mic_zc_freq",
+           "tran_zc_above_range", "vert_zc_above_range",
+           "long_zc_above_range", "mic_zc_above_range"]
+
+
+def test_fresh_db_has_zc_freq_columns(tmp_path: Path):
+    db = SeismoDb(tmp_path / "seismo_relay.db")
+    with sqlite3.connect(str(tmp_path / "seismo_relay.db")) as conn:
+        cols = {r[1] for r in conn.execute("PRAGMA table_info(events)").fetchall()}
+    for c in ZC_COLS:
+        assert c in cols, f"missing column {c}"
+
+
+def test_migration_adds_zc_freq_columns_to_legacy_db(tmp_path: Path):
+    db_path = tmp_path / "old.db"
+    # A "modern-minus-zc" events table (has blastware_* but not the zc columns).
+    with sqlite3.connect(str(db_path)) as conn:
+        conn.executescript("""
+            CREATE TABLE events (
+                id TEXT PRIMARY KEY, serial TEXT NOT NULL, waveform_key TEXT NOT NULL,
+                session_id TEXT, timestamp TEXT,
+                tran_ppv REAL, vert_ppv REAL, long_ppv REAL, peak_vector_sum REAL, mic_ppv REAL,
+                project TEXT, client TEXT, operator TEXT, sensor_location TEXT,
+                sample_rate INTEGER, record_type TEXT,
+                false_trigger INTEGER NOT NULL DEFAULT 0,
+                created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%SZ', 'now')),
+                UNIQUE(serial, timestamp)
+            );
+            INSERT INTO events (id, serial, waveform_key, timestamp)
+              VALUES ('legacy-id', 'BE11529', '01110000', '2026-04-01T12:00:00');
+        """)
+    db = SeismoDb(db_path)              # triggers _migrate
+    rows = db.query_events(serial="BE11529")
+    assert len(rows) == 1
+    for c in ZC_COLS:
+        assert c in rows[0]            # present
+        assert rows[0][c] is None      # NULL for the legacy row